gh-129824: Fix data race on runtime->gilstate.check_enabled

The new_interpreter() function can be called concurrently.

Author: colesbury

Python/pylifecycle.c

@@ -2435,7 +2435,7 @@ new_interpreter(PyThreadState **tstate_p,
 
     /* Issue #10915, #15751: The GIL API doesn't work with multiple
        interpreters: disable PyGILState_Check(). */
-    runtime->gilstate.check_enabled = 0;
+    _Py_atomic_store_int_relaxed(&runtime->gilstate.check_enabled, 0);
 
     // XXX Might new_interpreter() have been called without the GIL held?
     PyThreadState *save_tstate = _PyThreadState_GET();