refactor: Update devcontainer image name construction in test-devcont…

…ainer.yml

.github/workflows/test-devcontainer.yml

@@ -16,14 +16,16 @@ jobs:
       - name: Checkout (GitHub)
         uses: actions/checkout@v4
 
+      - uses: "./.github/shared/devcontainer-image-name"
+
       - name: use devcontainer image
         uses: devcontainers/ci@v0.3
         with:
           # commented out to explicitly USE the devcontainer image built by the build-devcontainer.yml workflow
           # imageName: ghcr.io/ionos-wordpress/ionos-wordpress-devcontainer
 
           # enable caching (will build the image only if related files where changed)
-          cacheFrom: ghcr.io/ionos-wordpress/ionos-wordpress-devcontainer
+          cacheFrom: ${{ env.IMAGE_NAME }}
 
           runCmd: |
             pnpm install