[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

jupyter_server/prometheus/server.py

@@ -234,7 +234,7 @@ def stop(self) -> None:
             self.http_server.stop()
             self.http_server = None
 
-        if hasattr(self, 'ioloop') and self.ioloop is not None:
+        if hasattr(self, "ioloop") and self.ioloop is not None:
             # Stop the IOLoop
             self.ioloop.add_callback(self.ioloop.stop)
             self.ioloop = None