Launching tests with Spring cloud no longer works

### Expected Behavior

Test should run

### Actual Behaviour

Test fails to start as rest plugin throws exception due to missing jwt secret

After the recent pr https://github.com/apache/grails-core/pull/14067 the change in grails-testing-support seems to cause issues when using Spring Cloud namely application.yml properties are not being merged properly

### Steps To Reproduce

Sample project at https://github.com/lynchie14/grails7configbug/tree/master

Run test-app -integration -echoOut and it will fail

Uncomment below in the build.gradle and force the library back to the M3 build and re-run it and it works again

// if (details.requested.group == 'org.grails' && details.requested.name == 'grails-testing-support'){
// details.useVersion '7.0.0-M3'
// }

### Environment Information

_No response_

### Example Application

https://github.com/lynchie14/grails7configbug/tree/master

### Version

grails-7.0.0-SNAPSHOT

Start with the linked sample project and run `test-app -integration -echoOut` to reproduce the REST plugin exception about the missing JWT secret. Compare the current grails-testing-support behavior with the forced 7.0.0-M3 build and inspect the build.gradle and application.yml configuration; done means the test starts successfully with the application properties merged.

Written by the indexing model from the issue text.