PR testing updates fails when there are workflow changes

Stream: nightly-testing

[Joachim Breitner]

https://github.com/leanprover/lean4/actions/runs/10389954160/job/28769250208 failed with

 ! [remote rejected]       lean-pr-testing-3160 -> lean-pr-testing-3160 (refusing to allow a Personal Access Token to create or update workflow `.github/workflows/bors.yml` without `workflow` scope)

I think this happens when lean-pr-testing-3160 already exists and there are changes to .github on nightly-testing.

This can be fixed by giving the PAT used here also the workflow scope. Does this bother anyone who can do this enough to do it?

[Kim Morrison]

Done, I think!

For future reference:

• login to github as leanprover-community-mathlib4-bot (credentials via the usual process)
• go to https://github.com/settings/tokens
• guess that lean4 MATHLIB4_BOT is the relevant token
• add workflow