Fix QNN llama script Python path

[JacobSzwejbka]

Summary:

Fix QNN llama CI scripts so they resolve EXECUTORCH_ROOT to the repository root and set PYTHONPATH to the parent of that root. The Qualcomm examples are source-tree modules, so the CI import path needs the repo parent instead of a cwd-relative '..'. This addresses failures such as:

python: No module named executorch.examples.qualcomm.oss_scripts.llama.eval_llama_qnn

Test Plan:

bash -n .ci/scripts/test_llama.sh .ci/scripts/test_qnn_static_llama_eval.sh .ci/scripts/test_qnn_static_llm.sh
git diff --check origin/main
lintrunner -r origin/main
Verified the new EXECUTORCH_ROOT expression resolves to the repo root for all three scripts.

Authored with Claude.

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20751

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

As of commit d44c8aa with merge base 6edd49d ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 512949f0cba74da0c5bdddeafc6331b6b63982cee14f337dcb2513aa2f83133d /exec failed with exit code 1
• trunk / unittest-release / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 18e53d79af7fd9e23c172675af05e30e30574ba8c7844fbb52f4eca1e3ae3ab0 /exec failed with exit code 1

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

• pull / unittest-nxp-neutron / linux-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 / linux / linux-job (gh) (trunk failure)

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