Update go-github from v37 -> v39

[pje]

Like #800, but also update imports to use the new version :)

I ran:

go get -u github.com/google/go-github/v39
rg --files-with-matches 'github.com/google/go-github/v37/github' **/*.go | xargs sed -i '' "s|github.com/google/go-github/v37/github|github.com/google/go-github/v39/github|g"
go mod tidy

In particular this pulls in the changes @mumoshu made in google/go-github#2103 that have since been merged into their main, so we no longer need the replace directive in go.mod.

[pje]

Can I help move this along in any way? Is there manual testing that needs to be done? Thanks!

[mumoshu]

@pje Sorry for the delay! I'm sure this will be a part of our next feature release (v0.21.0)

[pje]

@mumoshu no worries! Just wanted to know if I could help test or something. 👍

[mumoshu]

Thanks for your patience! Fixed conflicts and force-pushed to your branch. I'm now waiting for the build to pass 😄

[mumoshu]

All green! Merging. Thanks a lot for your support @pje ☺️