test: Fix flake with context.Cancelled in provisionerd

[kylecarbs]

This occurred because the context can cancel in the same time a response
is sent. This isn't a bug, because the complete still occurs.

https://github.com/coder/coder/runs/5366075943?check_suite_focus=true#step:7:56

[bryphe-coder]

Thanks for investigating these!

[codecov]

Codecov Report

Merging #386 (8a2270d) into main (fd5eceb) will increase coverage by 1.61%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #386      +/-   ##
==========================================
+ Coverage   66.10%   67.71%   +1.61%     
==========================================
  Files          71      150      +79     
  Lines         773     8475    +7702     
  Branches       72       72              
==========================================
+ Hits          511     5739    +5228     
- Misses        248     2155    +1907     
- Partials       14      581     +567     

Flag	Coverage Δ
unittest-go-macos-latest	66.17% <ø> (?)
unittest-go-ubuntu-latest	67.33% <ø> (?)
unittest-go-windows-2022	65.46% <ø> (?)
unittest-js	66.10% <ø> (ø)

Impacted Files	Coverage Δ
provisioner/terraform/parse.go	77.77% <0.00%> (ø)
database/migrate.go	52.38% <0.00%> (ø)
database/time.go	0.00% <0.00%> (ø)
httpmw/projectparam.go	76.47% <0.00%> (ø)
coderd/provisionerdaemons.go	57.29% <0.00%> (ø)
coderd/workspaceagent.go	37.36% <0.00%> (ø)
cli/projectplan.go	62.50% <0.00%> (ø)
coderd/cmd/root.go	82.43% <0.00%> (ø)
codersdk/files.go	66.66% <0.00%> (ø)
database/pubsub_memory.go	87.17% <0.00%> (ø)
... and 69 more

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