RFR: 8353596: GenShen: Test TestClone.java#generational-no-coops intermittent timed out

[William Kemper]

Clean backport. Fixes stuck thread issue.

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Commit messages:
 - Backport ac17449bdb946d98cb65c8eae9c9671f527a79cb

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/183/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=183&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353596
  Stats: 7 lines in 1 file changed: 1 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/183.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/183/head:pull/183

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/183