[llvm] Use container on Linux to run llvm-project-tests workflow (PR #81349)

[Tom Stellard via llvm-commits]

tstellar wrote:

> Do you have figures on how much this sped up the pipeline? Also, I'm assuming the plan is to enable this later for the other projects?

Build Time of llvm, clang, lld, and lldb (not including running lit tests):

[Without Container](https://github.com/tstellar/llvm-project/actions/runs/7855801404/job/21437883159): 146m 45s
[With Container](https://github.com/llvm/llvm-project/actions/runs/7852756732/job/21431586669?pr=81349): 109m 9s

So ~34% faster with the container


https://github.com/llvm/llvm-project/pull/81349