Currently, we have a number of rather complex regexes in .pre-commit-config.yaml that validate various invariants in the PEPs. We also have a script check-peps.py that does the same thing in Python. Not only does that script not require long incomprehensible regexes, it also provides much better error messages to users.

So we should ditch the regexes and just use check-peps.py. @hugovk tells me that when we tried, there was some issue with Windows (#4061 (comment)). Let's figure out what the issue was and fix it, so we can fully remove the regexes.