gh-93649: Undefine NDEBUG in Modules/_testcapi/* to enable assert() (GH-95793)

Author: encukou

Modules/_testcapi/parts.h

@@ -1,5 +1,8 @@
 #include "Python.h"
 
+/* Always enable assertions */
+#undef NDEBUG
+
 int _PyTestCapi_Init_Vectorcall(PyObject *module);
 int _PyTestCapi_Init_VectorcallLimited(PyObject *module);
 int _PyTestCapi_Init_Heaptype(PyObject *module);