generator frame type should not be PyObject*[]

[iritkatriel]

For historical reasons, the *_iframe field in _PyGenObject_HEAD is declared as PyObject*[], and later cast to _PyInterpreterFrame * (which is not a PyObject*).

Linked PRs

• gh-120834: fix type of *_iframe field in _PyGenObject_HEAD declaration #120835
• gh-120834: fix over-allocation in PyGenObject, PyCoroObject, PyAsyncGenObject. #120941
• gh-120834: Use PyGenObject for generators, coroutines and async generators #120976