Bump docker/build-push-action from 5 to 6 in the all group

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


Updates `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
  dependency-group: all
...

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

.github/workflows/test.yml

@@ -76,7 +76,7 @@ jobs:
       - name: Build image up to including stage 'build'
         id: image-build
         # note that the action's name is misleading: this step does NOT push
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           load: true # make the built image available in docker (locally)
@@ -191,7 +191,7 @@ jobs:
           path: sync/pidstat.txt
 
       - name: Build entire image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           load: true # make the built image available in docker (locally)
@@ -236,7 +236,7 @@ jobs:
 
       - name: Push entire image
         if: env.SHOULD_DEPLOY == 'true'
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           file: workflow-container/Dockerfile