Close PRs that try to merge a user's maintenance branch into master

[Mariatta]

Close PR that tries to merge the user's maintenance branch into CPython's master.

This will close PR like python/cpython#4266.

[codecov]

Codecov Report

Merging #70 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #70   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          14     14           
  Lines         923    931    +8     
  Branches       55     55           
=====================================
+ Hits          923    931    +8

Impacted Files	Coverage Δ
bedevere/close_pr.py	100% <100%> (ø)	⬆️
tests/test_close_pr.py	100% <100%> (ø)	⬆️

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[brettcannon]

Obviously keep a close eye on this one once you merge to make sure it doesn't over-reach.

[Mariatta]

Thanks!

[Mariatta]

Sorry!! I broke things, as seen in python/cpython#4409 🙇‍♀️ Will write another test case and a PR soon.

[brettcannon]

I had a feeling that regex might be too permissive. 😄 It's okay, I've just gone ahead and rolled back on Heroku to the last version so there's no rush.