make gh pr descrition as part of merge pr

[Gasoonjia]

this pr makes ghexport merge pr contains the description of origianl gh pr, so that we do not need to copy and paste diff number in the commit note to link back to our diff,

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13237

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❌ 1 New Failure, 1 Unrelated Failure

As of commit 6c9f276 with merge base 4ce7078 ():

NEW FAILURE - The following job has failed:

• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 2c851f993c5dcabb940aa6fa2d0eea9ef7fc2b8b237983ef6cc4efaa46b3fef3 /exec 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-openvino-linux / linux-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'quantized_decomposed' object has no attribute 'convert_element_type'

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