Update Gradle (Wrapper JAR) to 9.2.1

[ebbez]

Turned out the Wrapper JAR was still Gradle 8.6. This PR updates Gradle + the Gradle Wrapper JAR & scripts to 9.2.1.

[berry120]

Looks like there' a few other things changed here too, do these need changing or can we just update the jar path?

[ebbez]

I don't think the .gradlew(.bat) scripts necessarily need to change, but the script modifications were the result of running ./gradlew.bat wrapper --gradle-version 9.2.1 (the command to update the wrapper), so it might be nice to have those up-to-date as well.

It seems primarily that they added the SPDX license-identifier, changed something about resolving a path physically to the cd command (from previously the pwd command), and changed from classpath to executing the jar directly with --jar instead of --classpath. Doesn't seem to be doing too much changes.

But if it's preferred for the scripts to stay the same then I'll remove those modifications :)

[berry120]

Happy if that was the auto-update script :)