RFR: 8369571: Parallel: Use ThreadsClaimTokenScope in PSAdjustTask

[Francesco Andreuzzi]

On Fri, 10 Oct 2025 14:39:55 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Trivial lifting threads claim token logic into using the existing `ThreadsClaimTokenScope`.
> 
> Test: tier1

Marked as reviewed by fandreuzzi (Author).

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PR Review: https://git.openjdk.org/jdk/pull/27746#pullrequestreview-3324055955