Fix needless spinning in _PyMutex_LockTimed with zero timeout (gh-135872)

The free threading build could spin unnecessarily on `_Py_yield()` if the initial
compare and swap failed.

Python/lock.c

@@ -58,7 +58,7 @@ _PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags)
             return PY_LOCK_ACQUIRED;
         }
     }
-    else if (timeout == 0) {
+    if (timeout == 0) {
         return PY_LOCK_FAILURE;
     }