[llvm] [ci] limit parallel windows compile jobs to 24 (PR #93329)

[Lucile Rose Nihlen via llvm-commits]

lnihlen wrote:

I think the problem is this is all guesswork. I'm looking in to some of the performance monitoring steps suggested by others, to see if we can collect some actual data about what's going on with the Windows build servers. But, in the mean time, if builds are unreliable due to OOM, this may be a band-aid we can put on the problem until we have a more informed solution.

https://github.com/llvm/llvm-project/pull/93329