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

[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

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Commit messages:
 - Backport e27c4d463d920994b79b8163f063ad74f6ee5d59

Changes: https://git.openjdk.org/jdk11u-dev/pull/1239/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1239&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8268185
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 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