RFR: 8329898: Revert one use of markWord.is_unlocked back to is_neutral

[Stefan Karlsson]

On Tue, 9 Apr 2024 04:29:08 GMT, David Holmes <dholmes at openjdk.org> wrote:

> [JDK-8325303](https://bugs.openjdk.org/browse/JDK-8325303) changed a number of occurrences of `is_neutral` to `is_unlocked`, but one change in basicLock.cpp should not have been changed as it relates to the displaced markword.
> 
> This is a trivial change.
> 
> Testing:
>  - tiers 1-3 (sanity)
> 
> Thanks

Marked as reviewed by stefank (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/18684#pullrequestreview-1988295386