Use GITHUB_SERVER_URL to determine image registry

.forgejo/workflows/build.yaml

@@ -8,6 +8,12 @@ jobs:
   deploy:
     runs-on: cicd
     steps:
+      - name: Prepare
+        id: prep
+        run: |
+          registry="${{ env.GITHUB_SERVER_URL }}"
+          echo "registry=${registry#*://}" | tee "${GITHUB_OUTPUT}"
+
       - name: Checkout
         uses: actions/checkout@v4
 
@@ -22,7 +28,7 @@ jobs:
       - name: Push
         uses: 'https://github.com/redhat-actions/push-to-registry@v2'
         with:
-          registry: code.porucha.net
+          registry: ${{ steps.prep.outputs.registry }}
           image: ${{ steps.build.outputs.image }}
           tags: ${{ steps.build.outputs.tags }}
           username: ${{ vars.FORGEJO_USERNAME }}