Bump docker/build-push-action from 6.7.0 to 6.8.0 in the ci group

Bumps the ci group with 1 update: [docker/build-push-action](https://github.com/docker/build-push-action).


Updates `docker/build-push-action` from 6.7.0 to 6.8.0
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@5cd11c3...32945a3)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: ci
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/nightly.yml

@@ -24,7 +24,7 @@ jobs:
         with:
           buildkitd-flags: "--debug"
       - name: Build multi-arch container image
-        uses: docker/build-push-action@5cd11c3a4ced054e52742c5fd54dca954e0edd85 # v6.7.0
+        uses: docker/build-push-action@32945a339266b759abcbdc89316275140b0fc960 # v6.8.0
         with:
           push: false
           builder: ${{ steps.buildx.outputs.name }}

.github/workflows/release.yml

@@ -68,7 +68,7 @@ jobs:
             type=raw,value=${{ steps.prep.outputs.VERSION }}
       - name: Publish images
         id: build-push
-        uses: docker/build-push-action@5cd11c3a4ced054e52742c5fd54dca954e0edd85 # v6.7.0
+        uses: docker/build-push-action@32945a339266b759abcbdc89316275140b0fc960 # v6.8.0
         with:
           sbom: true
           provenance: true