Migrating kotlin-test to kotlin-test-junit5 explicitly

[Jolanrensen]

Fixes Gradle errors like:

org.gradle.internal.component.resolution.failure.exception.VariantSelectionByAttributesException: Unable to find a variant with the requested capability: coordinates 'org.jetbrains.kotlin:kotlin-test-framework-junit':
   - Variant 'compile' provides 'org.jetbrains.kotlin:kotlin-test:2.3.10'
   - Variant 'enforced-platform-compile' provides 'org.jetbrains.kotlin:kotlin-test-derived-enforced-platform:2.3.10'
   - Variant 'enforced-platform-runtime' provides 'org.jetbrains.kotlin:kotlin-test-derived-enforced-platform:2.3.10'
   - Variant 'javadoc' provides 'org.jetbrains.kotlin:kotlin-test:2.3.10'
   - Variant 'platform-compile' provides 'org.jetbrains.kotlin:kotlin-test-derived-platform:2.3.10'
   - Variant 'platform-runtime' provides 'org.jetbrains.kotlin:kotlin-test-derived-platform:2.3.10'
   - Variant 'runtime' provides 'org.jetbrains.kotlin:kotlin-test:2.3.10'
   - Variant 'sources' provides 'org.jetbrains.kotlin:kotlin-test:2.3.10'

These have started to appear around bumping to Kotlin 2.3.10