Update to KoTest 6

[sdelamo]

https://github.com/kotest/kotest/releases/tag/v6.0.4

[araysse]

Kotest 6.0.4 Incompatible with Current Micronaut Test Adapters and BOM – Migration Requires New Adapter and Build Changes

Summary:
Upgrading Kotest to 6.0.4 breaks compatibility with our current test adapters and build checks. This requires dedicated changes, not just a version bump.
Key Issues:

Adapter/API Breakage:
The current adapter (test-kotest5) is designed for Kotest 5 and uses specific APIs and behaviors that do not exist in Kotest 6.
Kotest 6 changes test model and result types, causing compilation and runtime errors.
BOM/Build Integration Problems:
The test-bom module fails with Kotest 6 due to stricter plugin and toolchain constraints in the new BOM.
Resolving plugin dependencies (in checkBom) leads to failure due to mismatched Gradle/Kotlin versions.

Conclusion
Kotest 6.0.4 is not a drop-in upgrade. The current adapter targets Kotest 5 APIs and the BOM/build logic resolves plugin metadata that becomes incompatible under Kotest 6. Supporting 6.x requires a new adapter module and coordinated updates to the BOM verification and plugin/Kotlin toolchain.

[scprek]

Interested in trying out https://kotest.io/docs/framework/concurrency6.html

[natalie-zamani]

Very interested to see this supported! Our apps would benefit quite a bit from the improved concurrency support, but Micronaut is holding us back currently from those benefits