[llvm] [lit] Use `.format()` over format strings literals (PR #155912)

[Vladimir Vereschaka via llvm-commits]

vvereschaka wrote:

> @vvereschaka, is it possible for me to test out whether this fixes the issue?
> 
> I attempted to test #154439 before submitting it, but it appeared that my branch needed to be from "llvm-project" (as opposed to my fork of "llvm-project") to be accepted by BuildBot.

@justinfargnoli not a problem, I'll test it on the buildbot locally

https://github.com/llvm/llvm-project/pull/155912