[executorch] create an extra session for backend infra test

[Gasoonjia]

Stack from ghstack (oldest at bottom):

• -> [executorch] create an extra session for backend infra test #18089
• [executorch] show backend test infra pass rate of CUDA backend to PyTorch HUD #17874
• [executorch][PR] add cuda backend to backend test infra #17873

Differential Revision: D96078481

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18089

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✅ You can merge normally! (1 Unrelated Failure)

As of commit 94878b5 with merge base f09bd55 ():

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• Test Metal Backend / export-model-metal-artifact (openai, whisper-large-v3-turbo, non-quantized) / macos-job (gh) (matched macos rule in flaky-rules.json)
  File doesn't exist

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