fix(web-app-taiga): correct path_join for taiga-local.py volume mount

Ensure docker-compose template uses proper path_join for taiga-local.py
to avoid malformed mount paths when docker_compose.directories.config
does not end with a trailing slash.

https://chatgpt.com/share/6968e9b8-7b8c-800f-b002-9a48a94f05ce

roles/web-app-taiga/templates/docker-compose.yml.j2

@@ -18,7 +18,7 @@
       - media-data:{{ TAIGA_VOLUME_MEDIA }}
       # - ./config.py:/taiga-back/settings/config.py
 {% if TAIGA_TAIGAIO_ENABLED | bool %}
-      - {{ docker_compose.directories.config }}taiga-local.py:/taiga-back/settings/local.py:ro
+      - {{ [docker_compose.directories.config,'taiga-local.py' ] | path_join }}:/taiga-back/settings/local.py:ro
 {% endif %}
 {% include 'roles/docker-container/templates/networks.yml.j2' %}
       taiga: