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

[Vlad Serebrennikov via llvm-commits]

Endilll wrote:

One thing to be aware of is https://learn.microsoft.com/en-us/cpp/build/reference/cgthreads-code-generation-threads?view=msvc-170:
> By default, cl.exe uses four threads, as if /cgthreads4 were specified.
 
As far as I can see, we don't override it anywhere. `/cgthreads1` should reduce the thread contention (ninja already launches enough to put all the cores to work), and, hopefully, RAM usage.

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