gh-101101: Fix test_code_extra to reset value for refleak test (gh-102350)

Author: corona10

Modules/_testcapi/code.c

@@ -92,7 +92,11 @@ test_code_extra(PyObject* self, PyObject *Py_UNUSED(callable))
         goto finally;
     }
     assert ((uintptr_t)extra == 77);
-
+    // Revert to initial code extra value.
+    res = PyUnstable_Code_SetExtra(test_func_code, code_extra_index, NULL);
+    if (res < 0) {
+        goto finally;
+    }
     result = Py_NewRef(Py_None);
 finally:
     Py_XDECREF(test_module);