Error preparing 4.20.0 release

[Gregor Zurowski]

Hi Everyone:

When trying to prepare the new 4.20.0 release, I am running into the
following error:

```
[ERROR] JDK 25+ is required for releases to ensure all multi-release
JAR layers (java-21, java-25) are compiled.
```

I want to make sure that this is intended before I proceed building
with Java 25.

Thanks,
Gregor