Use Java 21 LTS instead of Java 25 in GitHub Actions workflow

[patnelly]

Hello a'm Paulo

I noticed that the GitHub Actions workflow is currently using Java 25:

java-version: "25"

Since Java 25 is a preview/non-LTS release, it may introduce instability or breaking changes in CI over time.

I would like to update the workflow to use Java 21 (LTS), which provides long-term support, better stability, and is recommended for production environments.

Please let me know if I can proceed with this improvement. Thank you!

[SentryMan]

Two things

• non-LTS wouldn't introduce instability in a project like this
• java 25 is an LTS