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

[Michael Kruse via llvm-commits]

Meinersbur wrote:

@Endilll  I think this PR is to avoid OOM errors (Compiling Flang requires >8GB RAM per `.cpp`). msvc being multi-threaded (i.e. NOT specifying `/cgthreads1`) still enables more parallelism that those 24 compile jobs. In my experience, `/cgthreads` does not change memory usage.

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