RFR: 8375364: [macos] Some jpackage signing tests fail after JDK-8375240

[Thomas Schatzl]

Hi all,

  please review the changes to let `G1BuildCandidateRegionsTask` use `Atomic<T>`.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8375364

Changes: https://git.openjdk.org/jdk/pull/29339/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29339&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375364
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/29339.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29339/head:pull/29339

PR: https://git.openjdk.org/jdk/pull/29339