[crac] RFR: Fix lock usage in ReferenceQueue

[Radim Vansa]

In JDK 17 the locking used monitors, but in JDK 21 this class uses ReentrantLock. The change was not reflected during merge of new methods.

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Commit messages:
 - Fix lock usage in ReferenceQueue

Changes: https://git.openjdk.org/crac/pull/110/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=110&range=00
  Stats: 12 lines in 2 files changed: 7 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/crac/pull/110.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/110/head:pull/110

PR: https://git.openjdk.org/crac/pull/110