Doc preview didn't get built

[awf]

Was expecting to see doc preview for #23 at https://www.julia-vscode.org/docs/previews/PR23, but it hasn't arrived.

Drilling into https://github.com/julia-vscode/docs/pull/23/checks?check_run_id=1044713988 we see errors:

2020-08-29T08:32:55.2884560Z [command]julia --color=yes --project=docs/ docs/make.jl
2020-08-29T08:33:02.7677598Z [ Info: SetupBuildDirectory: setting up build directory.
2020-08-29T08:33:04.2157953Z [ Info: Doctest: running doctests.
2020-08-29T08:33:05.7605935Z [ Info: ExpandTemplates: expanding markdown templates.
2020-08-29T08:33:07.4394985Z [ Info: CrossReferences: building cross-references.
2020-08-29T08:33:08.9462921Z [ Info: CheckDocument: running document checks.
2020-08-29T08:33:09.4859345Z [ Info: Populate: populating indices.
2020-08-29T08:33:11.5542814Z [ Info: RenderDocument: rendering document.
2020-08-29T08:33:12.7381333Z [ Info: HTMLWriter: rendering HTML pages.
2020-08-29T08:33:18.4852059Z ┌ Info: Deployment criteria for deploying preview build from GitHub Actions:
2020-08-29T08:33:18.4852494Z │ - ✔ ENV["GITHUB_REPOSITORY"]="julia-vscode/docs" occurs in repo="github.com/julia-vscode/docs"
2020-08-29T08:33:18.4852734Z │ - ✔ ENV["GITHUB_REF"] corresponds to a PR number
2020-08-29T08:33:18.4853405Z │ - ✔ `push_preview` keyword argument to deploydocs is `true`
2020-08-29T08:33:18.4853754Z │ - ✔ ENV["GITHUB_ACTOR"] exists
2020-08-29T08:33:18.4853989Z │ - ✔ ENV["DOCUMENTER_KEY"] exists exists
2020-08-29T08:33:18.4854195Z └ Deploying: ✔
2020-08-29T08:33:20.6177344Z Initialized empty Git repository in /tmp/jl_eoVAZM/.git/
2020-08-29T08:33:20.7231956Z Failed to add the RSA host key for IP address '140.82.113.4' to the list of known hosts (/home/runner/.ssh/known_hosts).
2020-08-29T08:33:20.7820500Z Load key "/home/runner/work/docs/docs/docs/.documenter": invalid format
2020-08-29T08:33:20.7821047Z git@github.com: Permission denied (publickey).
2020-08-29T08:33:20.7831600Z fatal: Could not read from remote repository.
2020-08-29T08:33:20.7831717Z 
2020-08-29T08:33:20.7831821Z Please make sure you have the correct access rights
2020-08-29T08:33:20.7831917Z and the repository exists.
2020-08-29T08:33:20.7864969Z ┌ Error: Git failed to fetch git@github.com:julia-vscode/docs
2020-08-29T08:33:20.7865627Z │ This can be caused by a DOCUMENTER_KEY variable that is not correctly set up.
2020-08-29T08:33:20.7866189Z │ Make sure that the environment variable is properly set up as a Base64-encoded string
2020-08-29T08:33:20.7866629Z │ of the SSH private key. You may need to re-generate the keys with DocumenterTools.
2020-08-29T08:33:20.7867045Z └ @ Documenter ~/.julia/packages/Documenter/PLD7m/src/Documenter.jl:502
2020-08-29T08:33:21.3130674Z ┌ Error: Failed to push:
2020-08-29T08:33:21.3131727Z │   exception =
2020-08-29T08:33:21.3132079Z │    failed process: Process(`git fetch upstream`, ProcessExited(128)) [128]
2020-08-29T08:33:21.3132286Z │    
2020-08-29T08:33:21.3132492Z │    Stacktrace:
2020-08-29T08:33:21.3132739Z │     [1] pipeline_error at ./process.jl:525 [inlined]
2020-08-29T08:33:21.3133392Z │     [2] #run#565(::Bool, ::typeof(run), ::Cmd) at ./process.jl:440
2020-08-29T08:33:21.3133653Z │     [3] run at ./process.jl:438 [inlined]
2020-08-29T08:33:21.3134250Z │     [4] (::Documenter.var"#git_commands#24"{String,SubString{String},String,Array{Any,1},Bool,String,String})(::String) at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:500
2020-08-29T08:33:21.3134791Z │     [5] (::Documenter.var"#23#29"{String})() at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:598
2020-08-29T08:33:21.3135731Z │     [6] cd(::Documenter.var"#23#29"{String}, ::String) at ./file.jl:104
2020-08-29T08:33:21.3136174Z │     [7] #22 at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:598 [inlined]
2020-08-29T08:33:21.3136788Z │     [8] withenv(::Documenter.var"#22#28"{String,String}, ::Pair{String,String}) at ./env.jl:161
2020-08-29T08:33:21.3137282Z │     [9] (::Documenter.var"#21#27"{String,SubString{String},String})(::String, ::IOStream) at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:597
2020-08-29T08:33:21.3137725Z │     [10] mktemp(::Documenter.var"#21#27"{String,SubString{String},String}, ::String) at ./file.jl:611
2020-08-29T08:33:21.3138129Z │     [11] mktemp(::Function) at ./file.jl:609
2020-08-29T08:33:21.3138734Z │     [12] #git_push#18(::String, ::String, ::String, ::SubString{String}, ::String, ::Array{Any,1}, ::Bool, ::Documenter.GitHubActions, ::String, ::typeof(Documenter.git_push), ::String, ::String, ::String) at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:582
2020-08-29T08:33:21.3139320Z │     [13] #git_push at ./none:0 [inlined]
2020-08-29T08:33:21.3139599Z │     [14] #15 at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:456 [inlined]
2020-08-29T08:33:21.3140176Z │     [15] #mktempdir#18(::String, ::typeof(mktempdir), ::Documenter.var"#15#17"{SubString{String},String,String,String,String,String,String,Array{Any,1},Bool,Documenter.GitHubActions,String}, ::String) at ./file.jl:634
2020-08-29T08:33:21.3140626Z │     [16] mktempdir(::Function, ::String) at ./file.jl:632 (repeats 2 times)
2020-08-29T08:33:21.3141313Z │     [17] (::Documenter.var"#14#16"{String,String,String,String,String,Nothing,String,Array{Any,1},Bool,Documenter.GitHubActions,String})() at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:455
2020-08-29T08:33:21.3141921Z │     [18] cd(::Documenter.var"#14#16"{String,String,String,String,String,Nothing,String,Array{Any,1},Bool,Documenter.GitHubActions,String}, ::String) at ./file.jl:104
2020-08-29T08:33:21.3142528Z │     [19] #deploydocs#13(::String, ::String, ::String, ::String, ::String, ::Nothing, ::Nothing, ::String, ::String, ::Array{Any,1}, ::Bool, ::Documenter.GitHubActions, ::Bool, ::typeof(deploydocs)) at /home/runner/.julia/packages/Documenter/PLD7m/src/Documenter.jl:432
2020-08-29T08:33:21.3143040Z │     [20] (::Documenter.var"#kw##deploydocs")(::NamedTuple{(:repo, :push_preview),Tuple{String,Bool}}, ::typeof(deploydocs)) at ./none:0
2020-08-29T08:33:21.3143314Z │     [21] top-level scope at /home/runner/work/docs/docs/docs/make.jl:36
2020-08-29T08:33:21.3143554Z │     [22] include at ./boot.jl:328 [inlined]
2020-08-29T08:33:21.3144004Z │     [23] include_relative(::Module, ::String) at ./loading.jl:1105
2020-08-29T08:33:21.3144430Z │     [24] include(::Module, ::String) at ./Base.jl:31
2020-08-29T08:33:21.3145082Z │     [25] exec_options(::Base.JLOptions) at ./client.jl:287
2020-08-29T08:33:21.3145306Z │     [26] _start() at ./client.jl:460
2020-08-29T08:33:21.3145543Z └ @ Documenter ~/.julia/packages/Documenter/PLD7m/src/Documenter.jl:603
2020-08-29T08:33:22.8236487Z Cleaning up orphan processes