staging/recurrent: Only schedule loading tasks for enabled loaders

Otherwise, we schedule and fill-in queues which are not consumed. This then
escalates to spurious infra alerts.

Those loaders were stopped to avoid running too much loaders in the staging infra.

swh/values/staging/swh-cassandra.yaml

@@ -2177,6 +2177,12 @@ scheduler:
     enabled: true
     requestedMemory: 400Mi
     requestedCpu: 10m
+    visitTypes:
+    - cvs
+    - git
+    - git-checkout
+    - deposit
+    - svn
 
 journalClientCassandraChecksConfiguration:
   cls: kafka