8382933: Improve Shenandoah clone barrier tests

[earthling-amzn]

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Progress

• JDK-8382933 needs maintainer approval
• Change must not contain extraneous whitespace
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Issue

• JDK-8382933: Improve Shenandoah clone barrier tests (Enhancement - P4)

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/537/head:pull/537
$ git checkout pull/537

Update a local copy of the PR:
$ git checkout pull/537
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/537/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 537

View PR using the GUI difftool:
$ git pr show -t 537

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https://git.openjdk.org/jdk25u-dev/pull/537.diff

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[bridgekeeper]

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[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @earthling-amzn This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

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