build(deps): bump flexi_logger from 0.28.3 to 0.28.4

Bumps [flexi_logger](https://github.com/emabee/flexi_logger) from 0.28.3 to 0.28.4.
- [Changelog](https://github.com/emabee/flexi_logger/blob/master/CHANGELOG.md)
- [Commits](https://github.com/emabee/flexi_logger/commits)

---
updated-dependencies:
- dependency-name: flexi_logger
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>