Fetch tags for gisnav image so that docs can be built inside it [skip ci]

Author: hmakelin

.github/workflows/push_gisnav_images.yml

@@ -25,6 +25,8 @@ jobs:
         uses: actions/checkout@v3
         with:
           path: colcon_ws/src/gisnav
+          fetch-depth: 0  # need for building docs (conf.py git describe)
+          fetch-tags: True  # need for building docs (conf.py git describe)
 
       - name: Login to GHCR
         uses: docker/login-action@v2