build(deps): bump regex from 1.5.6 to 1.6.0 in /atcoder-problems-backend

Bumps [regex](https://github.com/rust-lang/regex) from 1.5.6 to 1.6.0.
- [Release notes](https://github.com/rust-lang/regex/releases)
- [Changelog](https://github.com/rust-lang/regex/blob/master/CHANGELOG.md)
- [Commits](rust-lang/regex@1.5.6...1.6.0)

---
updated-dependencies:
- dependency-name: regex
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]