[libcxx-commits] [libcxx] [libcxx] Install runner last when building CI containers (PR #148072)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne approved this pull request.

LGTM assuming this doesn't break `libcxx/utils/ci/run-buildbot-container`.

https://github.com/llvm/llvm-project/pull/148072