[llvm] [GitHub][docker] Add python3 venv package to CI container (PR #161024)

[Baranov Victor via llvm-commits]

https://github.com/vbvictor created https://github.com/llvm/llvm-project/pull/161024

I'm trying to make clang-format job run natively on `ci-ubuntu-24.04` container.
As it appears, It already has `clang-format-21.1.0`, `python3.12` installed, but `python3.12` needs `venv` to work properly, and Ubuntu asks for this package to be installed in the system to create venv.

FYI I hacked test-run with `--break-system-dependencies` and clang-format job runs a lot faster https://github.com/llvm/llvm-project/actions/runs/18064896361/job/51406365488#logs (skipping 1min long `clang-format` installation). Just don't look at "Initialize containers" taking 6min, it usually takes 15-20sec

>From f59aa9451da01a566aa51ef7896c77c299b7a778 Mon Sep 17 00:00:00 2001
From: Victor Baranov <bar.victor.2002 at gmail.com>
Date: Sun, 28 Sep 2025 00:19:29 +0300
Subject: [PATCH] [GitHub][docker] Add python3 venv package to CI container

---
 .github/workflows/containers/github-action-ci/Dockerfile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.github/workflows/containers/github-action-ci/Dockerfile b/.github/workflows/containers/github-action-ci/Dockerfile
index 1d3f5f9c35d7f..dc0c9cabc7f01 100644
--- a/.github/workflows/containers/github-action-ci/Dockerfile
+++ b/.github/workflows/containers/github-action-ci/Dockerfile
@@ -62,6 +62,7 @@ RUN apt-get update && \
     # Having a symlink from python to python3 enables code sharing between
     # the Linux and Windows pipelines.
     python3-pip \
+    python3-venv \
     file \
     tzdata \
     python-is-python3 && \