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/ci.yml

@@ -128,7 +128,7 @@ jobs:
           buildkitd-flags: --debug
       -
         name: Build
-        uses: docker/build-push-action@v2
+        uses: docker/build-push-action@v2.4.0
         with:
           context: .
           platforms: linux/amd64,linux/arm64,linux/ppc64le
@@ -274,7 +274,7 @@ jobs:
           config: /tmp/buildkitd.toml
       -
         name: Build
-        uses: docker/build-push-action@v2
+        uses: docker/build-push-action@v2.4.0
         with:
           context: .