The version specified by build.gradle is outdated:

Currently the correct version would be 2.8.8-SNAPSHOT.

However in general it might be good to drop Gradle as build tool, or only use Gradle (instead of Maven) in the future. Having to maintain two build tools increases maintenance work. For example Gradle builds currently do not seem to correctly include the project version in GsonBuildConfig.java, see:

• Fixed gradle build. #1554 (not sure if that pull request actually tries to fix that issue)
• Fix gradle build #1820

In case support for Gradle is dropped, the corresponding GitHub workflow (see #1648) can be removed again.