Reduce macOS CI cost

[metascroy]

Summary

[PLEASE REMOVE] See CONTRIBUTING.md's Pull Requests for ExecuTorch PR guidelines.

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Test plan

[PLEASE REMOVE] How did you test this PR? Please write down any manual commands you used and note down tests that you have written if applicable.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19678

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❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• Run pull request jobs on OSDC runners in shadow mode

❌ 3 New Failures, 1 Unrelated Failure, 1 Unclassified Failure

As of commit 5bd3606 with merge base f3387d0 ():

NEW FAILURES - The following jobs have failed:

• trunk / test-models-linux-aarch64 (add, portable, linux.arm64.2xlarge) / linux-job (gh)
  RuntimeError: Command docker exec -t 1ade77f380fe5948fcae9f2000cedbc6592755610a1891300bab4bbf471ef1eb /exec failed with exit code 1
• trunk / test-qnn-optimum-model (fp32, distilbert) / linux-job (gh)
  RuntimeError: Command docker exec -t 50666a07f85eb7d714094eb133fe53a701898173e5282db0b3611e36e3180be0 /exec failed with exit code 1
• trunk / unittest-release / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv2_model

UNCLASSIFIED FAILURE - DrCI could not classify the following job because the workflow did not run on the merge base. The failure may be pre-existing on trunk or introduced by this PR:

• Check Labels / Check labels (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: GraphQL query

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

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

• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_fp16_conv2d

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