ci: lowercase the ghcr image reference for the digest push

buildx's --output name= does no lowercasing (unlike metadata-action),
so ghcr.io/Gitlawb/node is an invalid reference and the per-arch digest
push would fail outright. Compute the lowercase image once in the
resolve step and reuse it, matching the manifest job.

Author: kevincodex1

.github/workflows/release.yml

@@ -92,6 +92,10 @@ jobs:
           esac
           echo "tag=$TAG" >> "$GITHUB_OUTPUT"
           echo "version=${TAG#v}" >> "$GITHUB_OUTPUT"
+          # ghcr requires a lowercase repository path, and unlike metadata-action,
+          # buildx's `--output name=` does no lowercasing — a mixed-case owner
+          # makes the digest push fail with "invalid reference format".
+          echo "image=ghcr.io/${GITHUB_REPOSITORY,,}" >> "$GITHUB_OUTPUT"
 
       - name: Checkout release tag
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -143,7 +147,7 @@ jobs:
           context: .
           platforms: ${{ matrix.platform }}
           provenance: false
-          outputs: type=image,name=ghcr.io/${{ github.repository }},push-by-digest=true,name-canonical=true,push=true
+          outputs: type=image,name=${{ steps.rel.outputs.image }},push-by-digest=true,name-canonical=true,push=true
           cache-from: type=gha,scope=docker-${{ matrix.arch }}
           cache-to: type=gha,mode=max,scope=docker-${{ matrix.arch }}