[jdk25u] RFR: 8361950: Update to use jtreg 8

[Aleksey Shipilev]

Upgrading jtreg to 8 to match mainline. It is a separate commit, so that we can backout jtreg 8 upgrade separately, if we need.

Additional testing:
 - [x] GHA
 - [ ] Linux AArch64 server fastdebug, `all` with jtreg-8+2

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Commit messages:
 - Backport 5db1dfe5c8b5df40779bb450849e6433aa9825ab

Changes: https://git.openjdk.org/jdk25u/pull/269/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=269&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361950
  Stats: 41 lines in 11 files changed: 9 ins; 19 del; 13 mod
  Patch: https://git.openjdk.org/jdk25u/pull/269.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/269/head:pull/269

PR: https://git.openjdk.org/jdk25u/pull/269