RFR: 8345750: Shenandoah: Test TestJcmdHeapDump.java#aggressive intermittent assert(gc_cause() == GCCause::_no_gc) failed: Over-writing cause

[William Kemper]

This is a clean backport and addresses a fairly critical issue where in a mistimed heap dump may cause heap corruption or vm crashes for Shenandoah GC.

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Commit messages:
 - Backport 6a29a8110ec38b4adc8163ba8651cbc935353f1d

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/151/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=151&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345750
  Stats: 23 lines in 4 files changed: 15 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/151.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/151/head:pull/151

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/151