CI: merge digest caches

.github/workflows/ci.yml

@@ -52,11 +52,13 @@ jobs:
         run: |
           mkdir -p /tmp/digests
           digest="${{ steps.build.outputs.digest }}"
+          cache_name="digests-${{ matrix.platform }}"
+          echo "CACHE_NAME=${cache_name/\//-}" >> $GITHUB_ENV
           touch "/tmp/digests/${digest#sha256:}"
       - name: Upload digest
         uses: actions/upload-artifact@v4
         with:
-          name: digests
+          name: ${{ env.CACHE_NAME }}
           path: /tmp/digests/*
           if-no-files-found: error
           retention-days: 1
@@ -69,8 +71,9 @@ jobs:
       - name: Download digests
         uses: actions/download-artifact@v4
         with:
-          name: digests
+          pattern: digests-*
           path: /tmp/digests
+          merge-multiple: true
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
       - name: Create Docker Image Label