RFR: 8378338: Shenandoah: Heap-used generic verification error after update-refs

[Aleksey Shipilev]

The generic verification is called at Final Update Refs. Shenandoah-specific verification for that step accounts for trash specially. But we enter in generic verification code and it does know about anything about it. So the fix is likely to relax generic verification, like we do in other cases. 

Additional testing:
 -  [x] Linux x86_64 server fastdebug, affected tests no longer fail with verification
 -  [ ] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/29843/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29843&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378338
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29843.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29843/head:pull/29843

PR: https://git.openjdk.org/jdk/pull/29843