[jdk24u] RFR: 8357550: GenShen crashes during freeze: assert(!chunk->requires_barriers()) failed

[William Kemper]

This is a low risk change that fixes an assertion failure with Shenandoah's generational mode and virtual threads. Only Shenandoah's generational mode is affected by this change.

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Commit messages:
 - Backport 17cf49746d0c289bdf779c974cdc84a3ab32ab4b

Changes: https://git.openjdk.org/jdk24u/pull/234/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk24u&pr=234&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357550
  Stats: 25 lines in 2 files changed: 25 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk24u/pull/234.diff
  Fetch: git fetch https://git.openjdk.org/jdk24u.git pull/234/head:pull/234

PR: https://git.openjdk.org/jdk24u/pull/234