RFR: 8253424: Add support for running pre-submit testing using GitHub Actions [v2]

[Andrew John Hughes]

> 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!

Andrew John Hughes has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into JDK-8253424
 - Merge remote-tracking branch 'origin/master' into JDK-8253424
 - 8241768: git needs .gitattributes
   
   Reviewed-by: erikj, jvernee, ehelin
 - Remove specification of minor version and package release data from GCC dependency
 - Fix JCheck tag regex
 - Backport 10029f784ef7be458a7b6ff3cc21649ff0abb6f3

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

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk8u/pull/3/files
  - new: https://git.openjdk.org/shenandoah-jdk8u/pull/3/files/0017a541..1cc5b2be

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk8u&pr=3&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk8u&pr=3&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk8u/pull/3.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk8u pull/3/head:pull/3

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