Bump docker/build-push-action from 3 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 3 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v3...v6)

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

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

.github/workflows/ci.yaml

@@ -53,7 +53,7 @@ jobs:
 
       - name: Docker build
         if: github.event_name != 'push' || !startsWith(github.ref, 'refs/tags/v')
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: false
@@ -64,7 +64,7 @@ jobs:
 
       - name: Docker build and push
         if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: true