[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 QNN 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

[pytorch-bot]

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

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⏳ No Failures, 60 Pending

As of commit b5c85f7 with merge base 48ba0a6 ():
💚 Looks good so far! There are no failures yet. 💚

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