fix(ci): use Docker network hostname for docs runner checkout

The act_runner and gitea containers share the git_default Docker
network. Use http://gitea:3000 (container DNS name) instead of
localhost, which resolves to the runner container itself.

.gitea/workflows/docs.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       - name: Checkout
         run: |
-          REPO_URL="http://localhost:3000/kindred/create.git"
+          REPO_URL="http://gitea:3000/kindred/create.git"
           if [ -d .git ]; then
             git fetch "$REPO_URL" main
             git checkout -f FETCH_HEAD