[libclang/python] type-ignore Any returns from library calls (llvm#…

…101310)

On its own, this change leads to _more_ strict typing errors as the
functions are mostly not annotated so far, so the `# type: ignore`s are
reported as Unused. This is part of the work leading up to llvm#78114
though, and one of the bigger parts factored out from it, so these will
later lead to less strict typing errors as the functions are annotated
with return types.