[llvm] [GitHub][CI] Run clang-format natively in ci-ubuntu container (PR #161073)

[Baranov Victor via llvm-commits]

vbvictor wrote:

> Removing the pip dependency cache (even if it doesn't hit unless it has been warmed on a PR) is probably going to be a significant regression.

I've checked ~10 different workflow runs ([runs.txt](https://github.com/user-attachments/files/22585137/runs.txt)) and on average it currently takes ~7sec to complete "Setup Python env + Install python dependencies" steps. In my test run, it took 6sec to "Create venv + install dependencies" so it could be even a speedup (or a very small regression)

Apart from it, I observed that `setup-python` works poorly inside docker environment and in the past I [failed](https://github.com/llvm/llvm-project/pull/154829#discussion_r2299002613) to set up custom python and caching for clang-tidy job.

To sum up for this PR, I think we either can merge without caching and see if we made a net-positive in [insights](https://github.com/llvm/llvm-project/actions/metrics/usage), or wait until a custom-container is made in https://github.com/llvm/llvm-project/pull/161083 so we wouldn't need any cache anymore.



https://github.com/llvm/llvm-project/pull/161073