Fix Docker image metadata output in CI

.gitea/workflows/ci.yml

@@ -43,11 +43,14 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Set image name (lowercase)
+      - name: Compute image metadata
         id: meta
+        env:
+          DOCKER_REGISTRY: ${{ secrets.DOCKER_REGISTRY }}
+          GITEA_REPOSITORY: ${{ gitea.repository }}
         run: |
-          IMAGE="${{ secrets.DOCKER_REGISTRY }}/${{ toLower(gitea.repository) }}"
-          echo "image=${IMAGE}" >> "$GITHUB_OUTPUT"
+          IMAGE="${DOCKER_REGISTRY}/$(printf '%s' "$GITEA_REPOSITORY" | tr '[:upper:]' '[:lower:]')"
+          echo "image=$IMAGE" >> "$GITHUB_OUTPUT"
 
       - name: Log in to Gitea container registry
         uses: docker/login-action@v3