fix: correct GHCR registry parameter in login step

The registry parameter was referencing env.GHCR_REGISTRY which no longer
exists after switching to hardcoded image names. This caused the login
to default to Docker Hub instead of GHCR, resulting in authentication
failures with GITHUB_TOKEN.

Now explicitly uses 'ghcr.io' as the registry parameter.

.github/workflows/build-and-release.yml

@@ -70,7 +70,7 @@ jobs:
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
         with:
-          registry: ${{ env.GHCR_REGISTRY }}
+          registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
@@ -147,7 +147,7 @@ jobs:
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
         with:
-          registry: ${{ env.GHCR_REGISTRY }}
+          registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}