Put matrix-media-repo.service in the matrix-media-repo group

Making the group match the Ansible task tags allows people to do `just install-service matrix-media-repo` and have that trigger both `--tags=matrix-media-repo` and also restart just that single group (`matrix-media-repo`).

group_vars/matrix_servers

@@ -326,7 +326,7 @@ devture_systemd_service_manager_services_list_auto: |
     +
     ([{'name': 'matrix-ma1sd.service', 'priority': 2000, 'groups': ['matrix', 'ma1sd']}] if matrix_ma1sd_enabled else [])
     +
-    ([{'name': (matrix_media_repo_identifier + '.service'), 'priority': 4000, 'groups': ['matrix', 'media_store']}] if matrix_media_repo_enabled else [])
+    ([{'name': (matrix_media_repo_identifier + '.service'), 'priority': 4000, 'groups': ['matrix', 'matrix-media-repo']}] if matrix_media_repo_enabled else [])
     +
     ([{'name': 'matrix-mailer.service', 'priority': 2000, 'groups': ['matrix', 'mailer']}] if matrix_mailer_enabled else [])
     +