[jdk11u-dev] RFR: 8268185: Update GitHub Actions for jtreg 6 [v5]

[George Adams]

> simple backport of [JDK-8268185](https://bugs.openjdk.java.net/browse/JDK-8268185): Update GitHub Actions for jtreg 6 in preparation for the GitHub action rewrite backport.

George Adams 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 three additional commits since the last revision:

 - Merge branch 'master' of https://git.openjdk.org/jdk11u-dev into jtreg6
 - Backport e27c4d463d920994b79b8163f063ad74f6ee5d59
 - Backport 3482cb87fd94e6445ca243722851daa90c00a2c8

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

Changes:
  - all: https://git.openjdk.org/jdk11u-dev/pull/1239/files
  - new: https://git.openjdk.org/jdk11u-dev/pull/1239/files/179d5224..493b8b13

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1239&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1239&range=03-04

  Stats: 63404 lines in 392 files changed: 35927 ins; 19780 del; 7697 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1239.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1239/head:pull/1239

PR: https://git.openjdk.org/jdk11u-dev/pull/1239