Bump CMake requirement to 3.29

[pytorchbot]

Summary

Update the CMake version requirement to 3.29. This is in response to XNNPACK implicitly requiring it.

Note that it should be sufficient to update the dependency only at the top-level CMake (as opposed to all of the separate locations where the version in specified).

Fixes #12524. See the issue for more context.

Test plan

I've built locally to verify that it builds correctly. CI will also help validate. I also attempted to build with an older CMake version (3.28), and observed the following error:

CMake Error at CMakeLists.txt:50 (cmake_minimum_required):
  CMake 3.29 or higher is required.  You are running version 3.28.0

Previously, it would error out with:

CMake Error at CMakeLists.txt:18 (CMAKE_POLICY):
  Policy "CMP0156" is not known to this version of CMake.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12690

• 📄 Preview Python docs built from this PR

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❌ 2 New Failures, 2 Cancelled Jobs

As of commit d4ec7a6 with merge base de24489 ():

NEW FAILURES - The following jobs have failed:

• pull / android / build-llm-demo / linux-job (gh)
  RuntimeError: Command docker exec -t d7b0e381e2b3fdee253b318f0c242cf10e665101bb3b769cf4c5ad3d82eb2404 /exec failed with exit code 2
• pull / test-eval_llama-mmlu-linux / linux-job (gh)
  RuntimeError: Command docker exec -t d2a12bf1aa53917d6ed819608446b1404ac08b94cbaecab25e0f05d8514080b9 /exec failed with exit code 1

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / test-models-linux (mobilebert, portable, linux.2xlarge) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-models-linux (mobilebert, xnnpack-quantization-delegation, linux.2xlarge) / linux-job (gh)
  ##[error]The operation was canceled.

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