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]>

.github/workflows/publish.yml

@@ -214,7 +214,7 @@ jobs:
         cp packages/Brian2*cp312-manylinux*_x86_64.whl dist
         cp packages/Brian2*cp312-manylinux*_aarch64.whl dist
     - name: Build (and potentially push) the Docker image
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       # https://github.com/docker/build-push-action
       with:
         context: .
@@ -227,7 +227,7 @@ jobs:
         labels: ${{ steps.meta.outputs.labels }}
     - name: Push docker image to dev repository
       if: ${{ github.repository == 'brian-team/brian2' && github.event_name == 'push' && !startsWith(github.ref, 'refs/tags') && github.actor != 'dependabot[bot]'}} 
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: .
         file: docker/Dockerfile