SpringBoot Gradle 6.9.x is not listed as a supported version when the Gradle version is < 6.8

An exception occurred applying plugin request [id: 'org.springframework.boot', version: '2.5.2-SNAPSHOT']
> Failed to apply plugin [id 'org.springframework.boot']
   > Spring Boot plugin requires Gradle 6.8.x or 7.x. The current version is Gradle 6.5.1

We should list 6.9.x as well.