RFR: 8352588: GenShen: Enabling JFR asserts when getting GCId

[William Kemper]

Clean backport, possibly related to https://bugs.openjdk.org/browse/JDK-8354431

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Commit messages:
 - Backport a2a64dac1680e97dd9eb511ead951bf1be8121c6

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/182/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=182&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352588
  Stats: 11 lines in 2 files changed: 4 ins; 7 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/182.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/182/head:pull/182

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/182