[clang] [libclang/python] Fix visitor callback return data type (PR #221024)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Generally LGTM! But this should come with a release note so users know about the fix. It should also come with a test which demonstrates the fix, if possible.

https://github.com/llvm/llvm-project/pull/221024