Pin LLVM 18.1.0 for JIT CI (Windows)

[savannahostrowski]

Looks like LLVM on Chocolatey has added 19.1.0 so we need to pin the JIT version.

Linked PRs

• GH-124398: Pin LLVM to 18.1.0 for JIT CI Windows #124399
• [3.13] GH-124398: Pin LLVM to 18.1.0 for Windows JIT CI (GH-124399) #129380