build(deps): bump fern from 0.6.0 to 0.6.1 in /atcoder-problems-backend

Bumps [fern](https://github.com/daboross/fern) from 0.6.0 to 0.6.1.
- [Release notes](https://github.com/daboross/fern/releases)
- [Changelog](https://github.com/daboross/fern/blob/main/CHANGELOG.md)
- [Commits](daboross/fern@fern-0.6.0...fern-0.6.1)

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

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

Author: dependabot[bot]