RFR: 8325093: Update CONTRIBUTING.md for build jdk version

[Ao Qi]

On Fri, 2 Feb 2024 13:37:15 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> [JDK-8297068](https://bugs.openjdk.org/browse/JDK-8297068) updated boot JDK to 19.0.1 from 18.0.2, and [JDK-8321434](https://bugs.openjdk.org/browse/JDK-8321434) updated boot JDK to 21.0.1. `CONTRIBUTING.md` should be updated correspondingly.
>
> Looks good. Thanks.

@kevinrushforth, thanks for the review.

-------------

PR Comment: https://git.openjdk.org/jfx/pull/1357#issuecomment-1924017692