[jdk25] RFR: 8357550: GenShen crashes during freeze: assert(!chunk->requires_barriers()) failed

[William Kemper]

This is a low risk change that addresses an assertion failure when Shenandoah's generational mode is used with virtual threads.

-------------

Commit messages:
 - Backport 17cf49746d0c289bdf779c974cdc84a3ab32ab4b

Changes: https://git.openjdk.org/jdk/pull/25918/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25918&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/jdk/pull/25918.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25918/head:pull/25918

PR: https://git.openjdk.org/jdk/pull/25918