Fix LLAMA app (#3228)

[kirklandsign]

Summary: Pull Request resolved: https://github.com/pytorch/executorch/pull/3228

Fix a UI thread issue causing crash.

Reviewed By: cccclai

Differential Revision: D56447006

fbshipit-source-id: 02eff27d4b4cd108c95b664d04679d4f92aaf5db (cherry picked from commit 4389442488f3f110ac74627439603a371e2f635f)

[pytorch-bot[bot]]

:link: Helpful Links

:test_tube: See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/3283

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:x: 3 New Failures

As of commit 3b5a01ce50941d44bb016c74987529706cd2e54e with merge base d3326a2073dee7baf78044fb3afd0772edbc616a ():

NEW FAILURES - The following jobs have failed:

• Apple / test-demo-ios / macos-job (gh) RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1
• Apple / upload-frameworks-ios (gh) Credentials could not be loaded, please check your action inputs: Could not load credentials from any providers
• Lint / lintrunner / linux-job (gh) >>> Lint for sdk/inspector/tests/inspector_test.py:

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[guangy10]

Android / test-demo-android (buck2) is failing