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

[Jannick Kremer via cfe-commits]

DeinAlptraum wrote:

@Endilll I rebased with the added tests from #109846 and checked with [diff-cover](https://pypi.org/project/diff-cover/) that all changed lines are covered by tests

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