Switch all remaining container volume mounting from -v to --mount

`--mount` is safer, as `-v` has the side-effect of creating the "source"
destination as a directory if it doesn't exist yet.
We don't need such magic.

roles/custom/matrix-bridge-hookshot/tasks/setup_install.yml

@@ -80,7 +80,7 @@
       --name={{ matrix_hookshot_container_url }}-validate
       --user={{ matrix_user_uid }}:{{ matrix_user_gid }}
       --cap-drop=ALL
-      -v {{ matrix_hookshot_base_path }}/config.yml:/config.yml
+      --mount type=bind,src={{ matrix_hookshot_base_path }}/config.yml,dst=/config.yml,ro
       {{ matrix_hookshot_docker_image }} node config/Config.js /config.yml
   register: hookshot_config_validation_result
   changed_when: false