Fix generate_workers_map script erroring out

I think this was accidentally removed before.

Testing strategy:
```
poetry run generate_workers_map --config-path homeserver.yaml
```

Author: MadLittleMods

synapse/_scripts/generate_workers_map.py

@@ -155,8 +155,8 @@ def get_registered_paths_for_default(
     hs = MockHomeserver(base_config, worker_app)
 
     # TODO We only do this to avoid an error, but don't need the database etc
+    hs.setup()
     registered_paths = get_registered_paths_for_hs(hs)
-
     hs.cleanup()
 
     return registered_paths