fix: lowercase image name for Docker registry cache reference

Author: MimoJanra

.github/workflows/docker-release.yml

@@ -19,6 +19,9 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
+      - name: Lowercase image name
+        run: echo "IMAGE_NAME=${IMAGE_NAME,,}" >> $GITHUB_ENV
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v4