Bump optimum-executorch pin to get optimization for cross attention

[larryliu0820]

As titled, so that we can include huggingface/optimum-executorch#187

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16485

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❌ 5 Cancelled Jobs, 1 Unrelated Failure

As of commit 1d3536f with merge base 6f57750 ():

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

• Lint / link-check / lint-file-size / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / unittest / linux / linux-job (gh)
• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / unittest-editable / linux / linux-job (gh)
  ##[error]The operation was canceled.

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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