AURORA-231: Upgrade gradle license plugin to v9 which contains reduced debug output

Upgrades license plugin to latest version which contains updates to
silence ignored headers [1].

[1]: https://github.com/hierynomus/license-gradle-plugin/pull/31

Testing Done:
./gradlew -Pq clean build

Bugs closed: AURORA-231

Reviewed at https://reviews.apache.org/r/22956/