RFR: 8332961: Parallel: Limit PSParallelCompact::verify_complete range

[Albert Mingkun Yang]

Trivial adjusting the verification range to skip regions in dense-prefix.

Test: checked the gc-log to see warnings are gone.

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Commit messages:
 - pgc-verify-dense-prefix

Changes: https://git.openjdk.org/jdk/pull/19409/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19409&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332961
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/19409.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19409/head:pull/19409

PR: https://git.openjdk.org/jdk/pull/19409