[clang] [libclang/python] Add check for reparsing (PR #172373)

[Jannick Kremer via cfe-commits]

https://github.com/DeinAlptraum approved this pull request.

LGTM
@Endilll do you think this requires a release note?
Technically it adds an error where there was none (where it was probably just failing if you did anything with the TU afterwards)

https://github.com/llvm/llvm-project/pull/172373