Bugfix use add_signal_handler not signal.signal

This fixes a848822 and ensures that
the event loop is woken and allowed to clean up on a signal, which
ensures that a correct cleanup occurs.

Author: pgjones

src/quart/app.py

@@ -1373,7 +1373,7 @@ def _signal_handler(*_: Any) -> None:
 
         for signal_name in {"SIGINT", "SIGTERM", "SIGBREAK"}:
             if hasattr(signal, signal_name):
-                signal.signal(getattr(signal, signal_name), _signal_handler)
+                loop.add_signal_handler(getattr(signal, signal_name), _signal_handler)
 
         server_name = self.config.get("SERVER_NAME")
         sn_host = None