Arm backend: Refactor test_scalars to new naming standard

[AdrianLundell]

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/10944

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❌ 1 New Failure, 1 Pending, 1 Unrelated Failure

As of commit c946d2a with merge base 54e7c75 ():

NEW FAILURE - The following job has failed:

• Apple / build-demo-ios / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-llava-runner-linux / linux-job (gh) (trunk failure)
  test_llava_export

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[AdrianLundell]

Errors unrelated, this is just a arm unittest change