Add return type annotation for Client._register_plugin (#9201)

Author: moi90

distributed/client.py

@@ -5123,7 +5123,7 @@ def _register_plugin(
         plugin: NannyPlugin | SchedulerPlugin | WorkerPlugin,
         name: str,
         idempotent: bool,
-    ):
+    ) -> Any:
         if isinstance(plugin, type):
             raise TypeError("Please provide an instance of a plugin, not a type.")
         if any(