gh-81057: Fix a Reference Leak in the posix Module (gh-100140)

The leak was introduced in gh-100082.

https://github.com/python/cpython/issues/81057

Modules/posixmodule.c

@@ -2242,6 +2242,7 @@ statresult_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         return NULL;
     }
     _posixstate *state = get_posix_state(mod);
+    Py_DECREF(mod);
     if (state == NULL) {
         return NULL;
     }