fix(hooks): match the post-checkout log prefix in the timeout fallback

The post-checkout body logs with [graphify] throughout, but the new
non-SIGALRM fallback used [graphify hook], so the same timeout read
differently depending on the platform. The post-commit body does use
[graphify hook] everywhere, so only the checkout copy was wrong.

Assert each body uses a single log prefix so this cannot drift again.

graphify/hooks.py

@@ -171,7 +171,7 @@ try:
             signal.alarm(_timeout)
         else:
             def _bail():
-                print(f'[graphify hook] graphify rebuild exceeded {_timeout}s', flush=True)
+                print(f'[graphify] graphify rebuild exceeded {_timeout}s', flush=True)
                 os._exit(1)
             _watchdog = threading.Timer(_timeout, _bail)
             _watchdog.daemon = True