[3.12] Add more C API tests (GH-112522) (GH-112525)

Add tests for PyObject_Str(), PyObject_Repr(), PyObject_ASCII() and
PyObject_Bytes().
(cherry picked from commit e0449b9a7fffc0c0eed806bf4cbb8f1f65397bbb)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>