[dagster webserver] fix websockets on py3.11 (#19328)

another place effected by
python/cpython#100458

the string `<GraphQLWS.PROTOCOL: 'graphql-ws'>` was being sent instead
of `graphql-ws`

## How I Tested These Changes

added assert to test that would have caught this

python_modules/dagster-webserver/dagster_webserver/graphql.py

@@ -182,7 +182,7 @@ async def graphql_ws_endpoint(self, websocket: WebSocket):
         """
         tasks: Dict[str, Task] = {}
 
-        await websocket.accept(subprotocol=GraphQLWS.PROTOCOL)
+        await websocket.accept(subprotocol=GraphQLWS.PROTOCOL.value)
 
         try:
             while (

python_modules/dagster-webserver/dagster_webserver_tests/test_subscriptions.py

@@ -1,6 +1,7 @@
 import gc
 import sys
 from contextlib import contextmanager
+from typing import Iterator
 from unittest import mock
 
 import objgraph
@@ -36,7 +37,7 @@
 
 
 @contextmanager
-def create_asgi_client(instance):
+def create_asgi_client(instance) -> Iterator[TestClient]:
     yaml_paths = [file_relative_path(__file__, "./workspace.yaml")]
 
     with WorkspaceProcessContext(
@@ -82,14 +83,15 @@ def example_job():
     example_op()
 
 
-def test_event_log_subscription():
+def test_event_log_subscription() -> None:
     with instance_for_test() as instance:
         run = example_job.execute_in_process(instance=instance)
         assert run.success
         assert run.run_id
 
         with create_asgi_client(instance) as client:
             with client.websocket_connect("/graphql", GraphQLWS.PROTOCOL) as ws:
+                assert str(ws.accepted_subprotocol) == "graphql-ws"
                 start_subscription(ws, EVENT_LOG_SUBSCRIPTION, {"runId": run.run_id})
                 gc.collect()
                 assert len(objgraph.by_type("async_generator")) == 1