Remove panic after graceful shutdown

remote-apis-testing shows the following log in
https://gitlab.com/remote-apis-testing/remote-apis-testing/-/jobs/2773967861

2022/07/26 20:20:14 Received terminated signal. Initiating graceful shutdown.
2022/07/26 20:20:14 Graceful shutdown complete
panic: Raising the original signal didn't cause us to shut down

Apparently, the panic line was reached before the signal had been
handled and the process killed, probably due to a different thread is
receiving the signal. For more details, see
golang/go#19326

pkg/global/graceful_termination_handler.go

@@ -49,7 +49,10 @@ func InstallGracefulTerminationHandler() (context.Context, *errgroup.Group) {
 		if err := process.Signal(receivedSignal); err != nil {
 			panic(err)
 		}
-		panic("Raising the original signal didn't cause us to shut down")
+		// This code should not be reached, if it weren't for the
+		// fact that process.Signal() does not guarantee that the
+		// signal is delivered to the same thread.
+		// More details: https://github.com/golang/go/issues/19326
 	}()
 
 	return ctx, &group