Bump docker/build-push-action from 2 to 2.4.0

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 2 to 2.4.0.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](https://github.com/docker/build-push-action/compare/v2...v2.4.0)

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/release.yml

@@ -18,7 +18,7 @@ jobs:
         with:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
-      - uses: docker/build-push-action@v2
+      - uses: docker/build-push-action@v2.4.0
         with:
           context: .
           file: server/Dockerfile
@@ -39,7 +39,7 @@ jobs:
         with:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
-      - uses: docker/build-push-action@v2
+      - uses: docker/build-push-action@v2.4.0
         with:
           context: .
           file: wikibase/Dockerfile