ctypes pointer set_type doesn't cache when setting _type_

[encukou]

Bug report

In #114314 (3.13) I introduced a regression: set_type misuses PyType_GetDict by modifying it.

import ctypes
intptr = ctypes.POINTER(ctypes.c_int)
print(intptr._type_)  # uncomment to hide the issue
print(intptr._type_)
intptr.set_type(ctypes.c_float)  # a bad idea, but, it should set _type_
print(intptr._type_)

Linked PRs

• gh-133290: Use PyObject_SetAttr to set _type_ #133292
• [3.13] gh-133290: Use PyObject_SetAttr to set _type_ (GH-133292) #133295