Backport of tests: Fixes a few data races in tests into release/1.9.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #25455 to be assessed for backporting due to the inclusion of the label backport/1.9.x.

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The person who merged in the original PR is:
@schmichael
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: POST https://api.github.com/repos/hashicorp/nomad/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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Description

Smattering of test only data race fixes. Individual commits have details, but the recurring theme is adding locking around peeking at internal shared struct fields.

Testing & Reproduction steps

go test -race

Links

Related to #12098 but unfortunately doesn't squash any of those.

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad website documentation to reflect this. Refer to
  the website README for docs guidelines. Please also consider whether the
  change requires notes within the upgrade guide.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

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Overview of commits

• 92de40b

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Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

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[schmichael]

Replaced by #25471

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