Use `merge_into` when adding workers to the shared config

docker/configure_workers_and_start.py

@@ -784,10 +784,9 @@ def generate_worker_files(
             {"name": worker_name, "port": str(worker_port), "config_path": config_path}
         )
 
-        # Update the shared config with any worker_type specific options. The first of a
-        # given worker_type needs to stay assigned and not be replaced.
-        worker_config["shared_extra_conf"].update(shared_config)
-        shared_config = worker_config["shared_extra_conf"]
+        # Update the shared config with any options needed to enable this worker.
+        merge_into(shared_config, worker_config["shared_extra_conf"])
+
         if using_unix_sockets:
             healthcheck_urls.append(
                 f"--unix-socket /run/worker.{worker_port} http://localhost/health"