PyGObject 3.9.2 Fixes Various Bugs

PyGObject 3.9.2 ports examples/option.py to Python 3 and GI, fixes the vfunc info search issue for classes with multiple inheritance, fixes closure argument conversion and marshaling Python to FFI return value for flags and enum. Moreover, PyGObject 3.9.2 removes usage of pyg_begin_allow_threads with Py_BEGIN_ALLOW_THREADS, a deprecated API for setting thread blocking functions, as well as half-implemented GC in PyGIStruct, PyGIBoxed, and PyGIBaseInfo.