Update docs about Gradle 9 compatibility #794
Description
Just noticed that Gradle 9 is not mentioned at:
- https://github.com/gradle/actions/blob/main/docs/dependency-submission.md#gradle-version-compatibility
- https://github.com/gradle/github-dependency-graph-gradle-plugin#gradle-compatibility
It's very likely compatible, but it looks strange that the last mention is 8.x.