push notifications: Fix unnecessary warning in development.

This prevents the warning about push notifications not being
registered for from being printed in development environment startup
by default.  In development, that's the expected state, and we don't
need to spam up the output with that notice.

zerver/lib/push_notifications.py

@@ -433,6 +433,9 @@ def push_notifications_enabled() -> bool:
 
 def initialize_push_notifications() -> None:
     if not push_notifications_enabled():
+        if settings.DEVELOPMENT and not settings.TEST_SUITE:  # nocoverage
+            # Avoid unnecessary spam on development environment startup
+            return
         logger.warning("Mobile push notifications are not configured.\n  "
                        "See https://zulip.readthedocs.io/en/latest/"
                        "production/mobile-push-notifications.html")