RFR: Build: Update to JDK 15.0.2

[Andrea Cosentino]

On Wed, 3 Feb 2021 10:12:09 GMT, Andrea Cosentino <github.com+5106647+oscerd at openjdk.org> wrote:

>> @oscerd you can just merge the `master` branch into your branch `jdk-15.0.2` (the merge commit will be automatically squashed when we integrate your changes, so don't worry). Then push the merge commit, then the GitHub Actions will be triggered ��
>
> Done

Thanks for helpin on the workflow. All seems to be ok.

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

PR: https://git.openjdk.java.net/skara/pull/989