ci: source build-job actions from github.com, not the forge mirror

The build job aborted during action preparation while cloning the docker/*
actions from code.forgejo.org (the checkout clone already warned "some refs
were not updated"). The check job proved that full github.com `uses:` URLs
clone reliably on this runner (mise-action@v2 worked), so pull checkout and the
docker actions from github.com directly. All are node20, which the runner
supports.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/deploy.yml

@@ -69,13 +69,13 @@ jobs:
     needs: [check]
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: https://github.com/actions/checkout@v4
 
       - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+        uses: https://github.com/docker/setup-buildx-action@v3
 
       - name: Login to the forge container registry
-        uses: docker/login-action@v3
+        uses: https://github.com/docker/login-action@v3
         with:
           # Forgejo auto-provides GITHUB_TOKEN to the job; it can push packages
           # for this repo's owner (uberbau). No external registry / PAT needed.
@@ -84,7 +84,7 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push container
-        uses: docker/build-push-action@v6
+        uses: https://github.com/docker/build-push-action@v6
         with:
           context: .
           push: true