Create single Github actions job to gate bors on

[nathanwhit]

This is a preliminary step for getting bors integrated into the chalk repo.

[jackh726]

Hmm. So how will this work will mdbook-linkcheck? I kind of feel like we shouldn't gate anything on it. Also, seems like it generates to separate checks (maybe one for stable and one for nightly test)

[nathanwhit]

Hmm. So how will this work will mdbook-linkcheck? I kind of feel like we shouldn't gate anything on it. Also, seems like it generates to separate checks (maybe one for stable and one for nightly test)

Makes sense to not gate on linkcheck, so I updated the workflow to reflect that.

As for the two checks (which was adopted from here as suggested by pietroalbini) it's actually intentional. As far as I know it's due to limitations in GHA, which make it so that you need to have two separate (and mutually exclusive) checks to accomplish what we need –– one check that just returns 0 if all other checks passed, and another that just returns 1 if any other check fails.

[jackh726]

Oh, duh. Right. Um, do they have to be named "bors build finished" or could they be "bors build finished success" and "bors build finished failed" to make them more clear

[nathanwhit]

As far as I know, I think they do need to have the same name (unfortunately).