Action Update: 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] <support@github.com>

.github/workflows/build-pypy.yml

@@ -45,7 +45,7 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Build Docker image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: "builder/"
           tags: ${{ env.BUILDER_IMAGE_TAG }}:${{ env.ALPINE_VERSION }}-${{ github.sha }}