Add Yolo26 to matrix of tested models on RISC-V

[luhenry]

Summary

It relates to #18833. It doesn't add Yolo on baremetal, but it at least makes sure that it works using Portable Kernels and XNNPACK backends.

Test plan

It's only adding a model to CI, so the CI is the test plan.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19741

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❌ 1 New Failure, 1 Cancelled Job, 1 Unrelated Failure

As of commit 02c7d69 with merge base 88eaf81 ():

NEW FAILURE - The following job has failed:

• pull / test-parakeet-xnnpack-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 6ff4eebc58915758ec47aaf5a473050aed7e4243ee04e6c35fb24fc2aafdcc1c /exec failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest / macos / macos-job (gh)

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)
  ##[error]The operation was canceled.

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[luhenry]

cc @rascani @mergennachin