Cleanup internal pack run

Author: stefanvanburen

conformance/test/server.py

@@ -48,7 +48,8 @@
     from google.protobuf.message import Message
 
 
-def pack(msg) -> Any:
+# TODO: Use google.protobuf.any.pack on upgrade to protobuf==6.
+def pack(msg: "Message") -> Any:
     any_msg = Any()
     any_msg.Pack(msg, type_url_prefix="'type.googleapis.com/'")
     return any_msg