Update GHCR push step to use Skopeo with zstd

Replaced the 'Push To GHCR' block with a new implementation using Skopeo for pushing images with zstd compression.

.github/workflows/build.yml

@@ -153,19 +153,28 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Push To GHCR
-        uses: redhat-actions/push-to-registry@5ed88d269cf581ea9ef6dd6806d01562096bee9c # v2
+            # Ersetze den gesamten "Push To GHCR" Block durch diesen hier:
+      - name: Push to GHCR with zstd using Skopeo
+        id: push  # Wir behalten die ID, falls spätere Schritte sie brauchen
         if: github.event_name != 'pull_request' && github.ref == format('refs/heads/{0}', github.event.repository.default_branch)
-        id: push
+        run: |
+          # Wir nutzen die Tags direkt aus dem metadata-Schritt
+          # Die Liste ist durch Leerzeichen getrennt, was Bash in der Schleife perfekt versteht.
+          for tag in ${{ steps.metadata.outputs.tags }}; do
+            echo "Pushing tag: $tag"
+            
+            # Quelle: Das lokal gebaute Image (ohne Registry-Präfix, wie in Buildah definiert)
+            # Ziel: Die vollständige URI (Registry + Name + Tag)
+            skopeo copy --compression zstd \
+              docker://${{ env.IMAGE_NAME }}:${{ env.DEFAULT_TAG }} \
+              ${{ env.IMAGE_REGISTRY }}/${{ env.IMAGE_NAME }}:$tag
+          done
         env:
-          REGISTRY_USER: ${{ github.actor }}
-          REGISTRY_PASSWORD: ${{ github.token }}
-        with:
-          registry: ${{ env.IMAGE_REGISTRY }}
-          image: ${{ env.IMAGE_NAME }}
-          tags: ${{ steps.metadata.outputs.tags }}
-          username: ${{ env.REGISTRY_USER }}
-          password: ${{ env.REGISTRY_PASSWORD }}
+          # Wir brauchen hier keine USER/PASS, da 'docker/login-action' bereits läuft
+          IMAGE_NAME: ${{ env.IMAGE_NAME }}
+          IMAGE_REGISTRY: ${{ env.IMAGE_REGISTRY }}
+          DEFAULT_TAG: ${{ env.DEFAULT_TAG }}
+
 
       # OPTIONAL: Image Signing with Cosign
       # Signing is disabled by default. To enable, see README.md "Optional: Enable Image Signing" section.