Enable testing MSC3874 in complement. (#14339)

docker/complement/conf/workers-shared-extra.yaml.j2

@@ -92,8 +92,6 @@ allow_device_name_lookup_over_federation: true
 ## Experimental Features ##
 
 experimental_features:
-  # Enable spaces support
-  spaces_enabled: true
   # Enable history backfilling support
   msc2716_enabled: true
   # server-side support for partial state in /send_join responses
@@ -104,6 +102,8 @@ experimental_features:
   {% endif %}
   # Enable jump to date endpoint
   msc3030_enabled: true
+  # Filtering /messages by relation type.
+  msc3874_enabled: true
 
 server_notices:
   system_mxid_localpart: _server