[clang] [libclang/python] Fix bugs in custom enum implementation and add tests (PR #95381)

[Jannick Kremer via cfe-commits]

DeinAlptraum wrote:

@Endilll I separated the fixes for the enum bugs from the strict typing PR, and added tests that cover these cases. I checked that the tests fail before the fixes and succeed now.

https://github.com/llvm/llvm-project/pull/95381