ci: add docker prune step to clean up Gitea runner cache after push

.gitea/workflows/staging.yaml

@@ -44,6 +44,12 @@ jobs:
         run: docker push gitea.hephex.de/daniel/webshop:staging
         working-directory: .
 
+      - name: Clean up runner Docker cache
+        run: |
+          docker image prune -f
+          docker builder prune -f
+        working-directory: .
+
 
       # KORREKTUR: IP-Adresse exakt auf Ihren Proxmox-Staging-Container eingestellt
       - name: Deploy to Proxmox LXC via SSH