gh-114827: clarify threading.Event.wait timeout behavior

Author: beauxq

Lib/threading.py

@@ -647,7 +647,8 @@ def wait(self, timeout=None):
         (or fractions thereof).
 
         This method returns the internal flag on exit, so it will always return
-        True except if a timeout is given and the operation times out.
+        True except if a timeout is given and the operation times out, when it
+        will return `False`.
 
         """
         with self._cond: