RFR: 8253424: Add support for running pre-submit testing using GitHub Actions

[Andrew John Hughes]

On Sun, 17 Apr 2022 15:12:42 GMT, Andrew John Hughes <andrew at openjdk.org> wrote:

> Hi all,
> 
> This pull request contains a backport of commit [10029f78](https://github.com/openjdk/jdk8u-dev/commit/10029f784ef7be458a7b6ff3cc21649ff0abb6f3) from the [openjdk/jdk8u-dev](https://git.openjdk.java.net/jdk8u-dev) repository, which enables GitHub Actions for the Shenandoah 8u fork.
> 
> The commit being backported was authored by Andrew John Hughes on 6 Apr 2022 and was reviewed by Severin Gehwolf.
> 
> Thanks!

@rkennke @shade could one of you review this please? It's a pretty straight-forward backport of the 8u changes to setup GitHub Actions so we can run build tests on merges of 8u332 & 8u342. Thanks.

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PR: https://git.openjdk.org/shenandoah-jdk8u/pull/3