Remove pinned buildkit version, add matrix.platform as an artifact path component and bump upload/download-artifact actions

Author: moritzheiber

.github/workflows/build-push.yaml

@@ -55,9 +55,6 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
       - uses: docker/setup-buildx-action@v3
-        with:
-          driver-opts: |
-            image=moby/buildkit:v0.19.0
       - uses: docker/build-push-action@v6
         name: Build
         id: build
@@ -77,20 +74,20 @@ jobs:
       - name: Export digest
         if: github.ref == 'refs/heads/main'
         run: |
-          mkdir -p /tmp/digests/${{ matrix.version }}-${{ matrix.image }}
+          mkdir -p /tmp/digests/${{ matrix.version }}-${{ matrix.image }}-${{ matrix.platform }}
           digest="${{ steps.build.outputs.digest }}"
-          touch "/tmp/digests/${{ matrix.version }}-${{ matrix.image }}/${digest#sha256:}"
+          touch "/tmp/digests/${{ matrix.version }}-${{ matrix.image }}-${{ matrix.platform }}/${digest#sha256:}"
       - name: Upload digest
         if: github.ref == 'refs/heads/main'
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
-          name: digests-${{ matrix.version }}-${{ matrix.image }}
-          path: /tmp/digests/${{ matrix.version }}-${{ matrix.image }}/*
+          name: digests-${{ matrix.version }}-${{ matrix.image }}-${{ matrix.platform }}
+          path: /tmp/digests/${{ matrix.version }}-${{ matrix.image }}-${{ matrix.platform }}/*
           if-no-files-found: error
           retention-days: 1
 
   merge-manifests:
-    needs: ["build-test-push", "gather-versions"]
+    needs: ["build-test-push"]
     if: github.ref == 'refs/heads/main'
     runs-on: ubuntu-24.04
     strategy:
@@ -105,14 +102,11 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
       - uses: docker/setup-buildx-action@v3
-        with:
-          driver-opts: |
-            image=moby/buildkit:v0.19.0
       - name: Download digests
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: digests-${{ matrix.version }}-${{ matrix.image }}
-          path: /tmp/digests/${{ matrix.version }}-${{ matrix.image }}
+          pattern: /tmp/digests/${{ matrix.version }}-${{ matrix.image }}-*
       - name: Create and push manifest
         working-directory: /tmp/digests/${{ matrix.version }}-${{ matrix.image }}
         run: |