Description:

The README mentions only the Java versions "8, 11, 16, 17, 21". [1]

Can you please explain the rationale for how it is decided to support a certain version or not?

I would additionally request adding support for all Java versions (at least going forward) because "The Tip & Tail Model of Library Development" [2] recommended by OpenJDK would require popular libraries to be able to build and release against the latest versions (as well as using older versions to verify compatibility of older releases).

[1] https://github.com/actions/setup-java/blob/main/README.md#supported-version-syntax
[2] https://openjdk.org/jeps/14

Justification:

Supporting more Java version will allow even more maintainers and vendors to be able to use this action for their builds.