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-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/ci.yaml

@@ -149,7 +149,7 @@ jobs:
           key: ${{ runner.os }}-buildx-nox-${{ matrix.arch }}-${{ matrix.os }}-${{ matrix.python }}
 
       - name: Build image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .github/containers/nox-cross-arch
           file: .github/containers/nox-cross-arch/${{ matrix.arch }}-${{ matrix.os }}-python-${{ matrix.python }}.Dockerfile
@@ -284,7 +284,7 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Test Installation
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           file: .github/containers/test-installation/Dockerfile