Add labeler for ARM path changes

[Sebastian-Larsson]

Apply module: arm and ciflow/trunk labels when backends/arm or examples/arm files are modified.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @robell

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18606

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❌ 1 New Failure, 3 Unrelated Failures

As of commit b31aa49 with merge base 07c5a54 ():

NEW FAILURE - The following job has failed:

• Apple / build-benchmark-app / macos-job (gh)

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

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

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / unittest-release / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[Sebastian-Larsson]

@digantdesai @SS-JIA we're looking for feedback on this new CI job that adds "module: arm" and "ciflow/trunk" automatically if arm files have been touched. Let us know what you think!

I also don't know how to properly test this so any help on that front would be appreciated