Modify galaxy ocp sample DB StorageClass

This commit modifies the DB StorageClass to workaround an issue
in prow pipeline and postgres pods crashing because of a
permission error:
```
chmod: changing permissions of '/var/lib/postgresql/data/pgdata': Operation not permitted
```

[noissue]

config/samples/pulpproject_v1beta1_pulp_cr.galaxy.ocp.ci.yaml

@@ -55,4 +55,4 @@ spec:
   file_storage_size: "5Gi"
   file_storage_storage_class: azurefile-csi
   database:
-    postgres_storage_class: azurefile-csi
+    postgres_storage_class: managed-csi