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/build-images.yml

@@ -55,7 +55,7 @@ jobs:
       run: make -C untested_base PYTHON_VERSION="${{ matrix.pyver }}" Dockerfile_dev Dockerfile_empty
     - name: Build dev_base
       id: dev_base
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: untested_base
         file: untested_base/Dockerfile_dev
@@ -70,7 +70,7 @@ jobs:
         cache-from: type=registry,ref=${{ steps.names.outputs.dev }}:cache_${{ steps.names.outputs.vertag }}
     - name: Build empty_base
       id: empty_base
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: untested_base
         file: untested_base/Dockerfile_empty
@@ -86,7 +86,7 @@ jobs:
     - name: Generate Final Dockerfile
       run: make -C untested_base PYTHON_VERSION="${{ matrix.pyver }}" DEV_TAG="${{ steps.names.outputs.dev }}@${{ steps.dev_base.outputs.digest }}" EMPTY_TAG="${{ steps.names.outputs.empty }}@${{ steps.empty_base.outputs.digest }}" Dockerfile_final
     - name: Build untested_base
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: untested_base
         file: untested_base/Dockerfile_final
@@ -102,7 +102,7 @@ jobs:
     - name: Test image
       run: docker run --rm "${{ steps.names.outputs.untested }}:${{ steps.names.outputs.vertag }}" /root/test.sh
     - name: Build base
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       if: ${{ matrix.main }}
       with:
         context: base