Could we put the black reformats into a separate PR? Remember that the commit message becomes a changelog entry for third-party stubs. (Something I always forget when merging.)

Could we put the black reformats into a separate PR? Remember that the commit message becomes a changelog entry for third-party stubs. (Something I always forget when merging.)

Yes, makes sense

The third-party stubtest failure in beautifulsoup has already been noted in #9645, and is unrelated to this PR.

The changes to builtins.BaseExceptionGroup.__init__ and builtins.ExceptionGroup.__init__ are needed to satisfy a new pyright lint: see https://github.com/python/typeshed/actions/runs/4063554162/jobs/6995928535. These methods are actually overridden at runtime, from what I can see, so it seems fine to override them in the stub as well: https://github.com/python/cpython/blob/75227fba1dd1683289d90ada7abba237bff55d14/Objects/exceptions.c#L808-L819

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉