README: update the `java-version` list

Description:
Java LTS version 21 has been available for some time now, but the repository is still not updated.

Justification:
Version 21 deserves to be in the list as an LTS version.

Are you willing to submit a PR?
No, sorry.

[SethTisue]

Doesn't it already work? I'm using it at e.g. https://github.com/SethTisue/Project-Euler/blob/main/.github/workflows/ci.yml and in a number of other repos I do work in.

Doesn't it already work? I'm using it at e.g. https://github.com/SethTisue/Project-Euler/blob/main/.github/workflows/ci.yml and in a number of other repos I do work in.

Yes, it can be used. It just hasn't been tested.

It's also not in the README, but you do have access to it.

[IvanZosimov]

Hi, @exhviewer 👋 As @SethTisue mentioned, Temurin 21 can be set up in the current version of setup-java. Nevertheless, thank you for the issue, we will update documentation.

[Khant-NyarxG-Next]

i want to make with kotlin
compileOptions {
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
}

i try so many way but don't worked

[IvanZosimov]

Hi, @Khant-NyarxG-Next 👋 Could you please create a new issue with the full context? Currently, it's not quite clear what problem you're trying to report.

[Khant-NyarxG-Next]

Hi, @Khant-NyarxG-Next 👋 Could you please create a new issue with the full context? Currently, it's not quite clear what problem you're trying to report.

thanks for response but i have been solve the problem .i create ci for my kotlin app and in yout docs i don't find the correct version of java and i found the solution from somewhere and it worked with
distribution: temurin
java-version: 21

[AleksandarTokarev]

It would be great if the README is updated with Java 21 - so people are not mislead that it does not work with Java 21.