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/build.yml

@@ -43,7 +43,7 @@ jobs:
           esac;
 
       - name: build & push image
-        uses: docker/build-push-action@v2
+        uses: docker/build-push-action@v2.4.0
         with:
           context: .
           file: docker/alpine/Dockerfile