Grails 7: Update grails-forge to Micronaut 4.x.x

[jamesfredley]

grails-forge is a Micronaut app

• Micronaut to 4.6.x
• Groovy to 4.0.x

This update is complex because Grails is no longer providing micronaut dependency versions and micronaut-bom is now io.micronaut.platform:micronaut-platform. This also involves javax to jakarta transitions and providing these dependencies. You will need to add micronaut-serde-jackson for micronaut-http.

spock complains about Gradle still using Groovy 3, in the test-core subproject.

Add Java 23 to matix.java:
https://github.com/grails/grails-forge/pull/400/files#diff-4c087648fbb704b0cc106eebfff7779856a6af4a6987e919debdd3afd1fdf7bbR15