[clang] [libclang/python] Do not rely on `ctypes`' `errcheck` (PR #105490)

[Jannick Kremer via cfe-commits]

https://github.com/DeinAlptraum commented:

@Endilll tested how exactly?
All tests still pass, obviously, but I just checked and there are six lines changed here, that are not currently covered by tests:
`Diagnostic.format()`, `Cursor.get_definition()`, `Cursor.get_usr()`, `Type.get_result()`, `Type.get_class_type()`, `Type.get_named_type()`

Should I add tests for all of these first, and then merge that into this PR?

https://github.com/llvm/llvm-project/pull/105490