Change Java 25 to default JVM testing

[sarahchen6]

What Does This Do

Change Java 25 to be a default JVM for testing. Remove "stable" testing, as the latest stable version is LTS v25.

Motivation

Additional Notes

This PR is in prep for Java 25 GA release some time this month. The build will not pass until the new image is added to https://github.com/DataDog/dd-trace-java-docker-build - the image is currently set to 25-09 which I expect to include Java 25. Afterwards, CI will need to be re-triggered.

Contributor Checklist

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Jira ticket: https://datadoghq.atlassian.net/browse/LANGPLAT-83