[ci] Look on pytorch servers when installing pip deps

[dbort]

Stack from ghstack (oldest at bottom):

• -> #3477

• 3476

• 3475

• 3474

• 3473

• 3472

• 3471

• 3470

• 3469

• 3468

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• 3466

When installing the executorch pip package for CI jobs, look on the pytorch servers when resolving dependencies. This lets the executorch package depend on pytorch pre-release and nightly versions.

Also run the llava setup with -x to make it easier to debug failures.

Differential Revision: D56857486

[pytorch-bot[bot]]

:link: Helpful Links

:test_tube: See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/3477

• :page_facing_up: Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

:x: 1 New Failure

As of commit 20168de96f94872db7cf19a3f3f930a464c58aab with merge base 5d2a17b29f57ab77f0481ca1d96d827e610dc4bf ():

NEW FAILURE - The following job has failed:

* [Android / test-llama-app / mobile-job (android)](https://hud.pytorch.org/pr/pytorch/executorch/3477#24487479388) ([gh](https://github.com/pytorch/executorch/actions/runs/8916102493/job/24487479388)) `Process completed with exit code 1.`

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@dbort merged this pull request in pytorch/executorch@aee435df98632f1dc6cc2acbbb621ff2c492e161.