Bump docker/build-push-action from 3 to 4

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 3 to 4.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v3...v4)

---
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/docker.yml

@@ -48,7 +48,7 @@ jobs:
       #### build+export, test only on PRs
       - name: Build and export to Docker
         if: github.event_name == 'pull_request'
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v4
         with:
           context: .
           file: docker/Dockerfile
@@ -84,7 +84,7 @@ jobs:
       #     password: ${{ secrets.GHCR_IO_REGISTRY_TOKEN }}
 
       - name: Build and push
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v4
         if: ${{ github.ref == 'refs/heads/master' || startsWith(github.ref, 'refs/tags') }}
         with:
           context: .