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

[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!

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

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

Changes: https://git.openjdk.java.net/shenandoah-jdk8u/pull/3/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah-jdk8u&pr=3&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253424
  Stats: 3402 lines in 4 files changed: 3402 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/shenandoah-jdk8u/pull/3.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah-jdk8u pull/3/head:pull/3

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