Log Message:
py-cython: updated to 0.29.15

0.29.15:
* Crash when returning a temporary Python object from an async-def function.
* Crash when using ``**kwargs`` in generators.
* Double reference free in ``__class__`` cell handling for ``super()`` calls.
* Compile error when using ``*args`` as Python class bases.
* Import failure in IPython 7.11.
* Fixed C name collision in the auto-pickle code.
* Deprecated import failed in Python 3.9.