fix(auth): remove unused type: ignore comment in _channel.py

Co-Authored-By: Claude <noreply@anthropic.com>

Author: zeevdr

sdk/src/opendecree/_channel.py

@@ -17,7 +17,7 @@
 def _token_call_credentials(token: str) -> grpc.CallCredentials:
     """Return gRPC call credentials that inject a Bearer token."""
 
-    def _callback(context: object, callback: object) -> None:  # type: ignore[type-arg]
+    def _callback(context: object, callback: object) -> None:
         assert callable(callback)
         callback([("authorization", f"Bearer {token}")], None)