Forward fix for broken update and attend test

[kiymetakdemir]

Summary:
[executorch] Add missing exir:_warnings dep to llm cache library

The cache python_library sources reference_cache.py, which imports
from executorch.exir._warnings import experimental for the experimental decorators on CacheConfig and ContiguousReferenceCache. The target only
depended on //caffe2:torch, so executorch.exir was absent at runtime and every test in test_update_and_attend failed at import with
ModuleNotFoundError: No module named 'executorch.exir'.

Add //executorch/exir:_warnings to the cache library's deps.

Reviewed By: metascroy

Differential Revision: D113428489

[pytorch-bot]

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❌ 2 New Failures

As of commit 3b579dc with merge base 179c4ee ():

NEW FAILURES - The following jobs have failed:

• Cadence Build & Test / hifi-build / hifi4 (gh)
  Refusing to check out fork pull request code from a 'pull_request_target' workflow. This workflow runs with the base repository's GITHUB_TOKEN, secrets, default-branch cache scope, and runner access. Fetching and executing a fork's code in that trusted context commonly leads to "pwn request" vulnerabilities. To opt in, review the risks at https://gh.io/securely-using-pull_request_target and set 'allow-unsafe-pr-checkout: true' on the actions/checkout step.
• Cadence Build & Test / vision-build / vision (gh)
  Refusing to check out fork pull request code from a 'pull_request_target' workflow. This workflow runs with the base repository's GITHUB_TOKEN, secrets, default-branch cache scope, and runner access. Fetching and executing a fork's code in that trusted context commonly leads to "pwn request" vulnerabilities. To opt in, review the risks at https://gh.io/securely-using-pull_request_target and set 'allow-unsafe-pr-checkout: true' on the actions/checkout step.

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[meta-codesync]

@kiymetakdemir has exported this pull request. If you are a Meta employee, you can view the originating Diff in D113428489.

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