Iterate through set of apps in extension_manager.any_activity method (

#1157)

Fixes #1156

jupyter_server/extension/manager.py

@@ -404,6 +404,7 @@ async def stop_all_extensions(self):
 
     def any_activity(self):
         """Check for any activity currently happening across all extension applications."""
-        for _, app in sorted(dict(self.extension_apps).items()):
-            if app.current_activity():
-                return True
+        for _, apps in sorted(dict(self.extension_apps).items()):
+            for app in apps:
+                if app.current_activity():
+                    return True