Fix S3 migration timer restart guard for non-Synapse setups

Only queue matrix-synapse-s3-storage-provider-migrate.timer for restart when Synapse is actually enabled. This prevents setup/install failures when a Synapse-only extension flag is set while using another homeserver implementation, as reported in https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4959.

group_vars/matrix_servers

@@ -833,7 +833,7 @@ devture_systemd_service_manager_services_list_auto: |
       'priority': 5000,
       'restart_necessary': true,
       'groups': ['matrix'],
-    }] if matrix_synapse_ext_synapse_s3_storage_provider_enabled else [])
+    }] if (matrix_synapse_enabled and matrix_synapse_ext_synapse_s3_storage_provider_enabled) else [])
     +
     ([{
       'name': 'matrix-synapse-auto-compressor.timer',