[Backend Tester] Add error message field to CSV report

[GregoryComer]

Include a (truncated) error message in the CSV. This should make it easier to parse at a glance.

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [Backend Tester] Increase linux runner size #14200
• [Backend Tester] Add ARM TOSA flow #14190
• [Backend Tester] Skip tests with undelegated conv3d ops #14185
• [Backend Tester] Refactor workflows into one workflow per backend #14137
• [Backend Tester] Add flow-specific skipped tests, skip argmin/max on Core ML due to native crashes, float16/64 on Vulkan #13992
• -> [Backend Tester] Add error message field to CSV report #13991
• [Backend Tester] Skip inf and nan operator tests #13990
• [Backend Tester] Skip in-place activation tests due to lack of support in ET #13989

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13991

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❌ 1 New Failure, 5 Cancelled Jobs, 2 Unrelated Failures

As of commit bd5faf0 with merge base 6d8583d ():

NEW FAILURE - The following job has failed:

• pull / test-eval_llama-wikitext-linux / linux-job (gh)
  RuntimeError: Command docker exec -t e1fcd4084154f10e1a0d769409c6baae51bc7726fcf813fe430b5e47a735daf1 /exec failed with exit code 1

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / test-binary-size-linux-gcc / linux-job (gh)
• pull / test-llava-runner-linux / linux-job (gh)
• pull / test-models-linux (phi_4_mini, portable, linux.4xlarge.memory) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-moshi-linux / linux-job (gh)
• pull / test-openvino-linux / linux-job (gh)

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• nightly / backend-test-linux (qnn_16a16w, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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

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

• pull / test-setup-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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