Bump spotless-maven-plugin from 2.13.1 to 2.15.0

Bumps [spotless-maven-plugin](https://github.com/diffplug/spotless) from 2.13.1 to 2.15.0.
- [Release notes](https://github.com/diffplug/spotless/releases)
- [Changelog](https://github.com/diffplug/spotless/blob/main/CHANGES.md)
- [Commits](https://github.com/diffplug/spotless/compare/lib/2.13.1...lib/2.15.0

)

---
updated-dependencies:
- dependency-name: com.diffplug.spotless:spotless-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>