Bump docker/build-push-action from 5 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 5 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v5...v6)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -86,15 +86,15 @@ jobs:
           images: ghcr.io/${{ steps.lowercase.outputs.owner }}/${{ steps.lowercase.outputs.repo }}
 
       - name: Build and push client image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: true
           tags: ghcr.io/${{ steps.lowercase.outputs.owner }}/${{ steps.lowercase.outputs.repo }}/client:latest
           target: client
 
       - name: Build and push server image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: true