gh-146527: Fix memory leak in _PyGC_Fini() (#150969)

Free generation_stats allocated by _PyGC_Init().

Fix Python/gc.c: Python/gc_free_threading.c was already fixed.

Author: vstinner

Python/gc.c

@@ -1876,6 +1876,8 @@ _PyGC_Fini(PyInterpreterState *interp)
     GCState *gcstate = &interp->gc;
     Py_CLEAR(gcstate->garbage);
     Py_CLEAR(gcstate->callbacks);
+    PyMem_RawFree(gcstate->generation_stats);
+    gcstate->generation_stats = NULL;
 
     /* Prevent a subtle bug that affects sub-interpreters that use basic
      * single-phase init extensions (m_size == -1).  Those extensions cause objects