fix(ci): use localhost:3000 for docs runner checkout

The docs runner is on the same host as Gitea, so clone via
http://localhost:3000 instead of the public HTTPS URL which
fails to connect (port 443 unreachable from the runner).

.gitea/workflows/docs.yml

@@ -13,11 +13,12 @@ jobs:
     steps:
       - name: Checkout
         run: |
+          REPO_URL="http://localhost:3000/kindred/create.git"
           if [ -d .git ]; then
-            git fetch origin main
-            git checkout -f origin/main
+            git fetch "$REPO_URL" main
+            git checkout -f FETCH_HEAD
           else
-            git clone --depth 1 --branch main https://git.kindred-systems.com/kindred/create.git .
+            git clone --depth 1 --branch main "$REPO_URL" .
           fi
 
       - name: Build mdBook