Pre-release cleanup

[sgdc3]

This is a quick cleanup clean things up before the 5.6.0 release

[ljacqu]

AsynchronousUnregisterTest, GeoIpServiceTest -> failing because of Mockito. I'm on it ;)

Edit: done

[ljacqu]

Changes look good to me.

• Probably need to add the released datasourcecolumns to plugin.yml's libraries
• The build from GitHub Actions is failing because it's using an incompatible Maven version

[sgdc3]

@ljacqu tests on JDK 21 are failing, should we fix that or just skip JDK 21 in the pipeline?

[ljacqu]

tests on JDK 21 are failing, should we fix that or just skip JDK 21 in the pipeline?

Fixed (I think)