Upgrade LLVM to 19.1.0 in pip package (#8423)

Author: alexreinking

.github/workflows/pip.yml

@@ -12,7 +12,7 @@ on:
 
 env:
   # TODO: detect this from repo somehow: https://github.com/halide/Halide/issues/8406
-  LLVM_VERSION: 18.1.8
+  LLVM_VERSION: 19.1.0
   FLATBUFFERS_VERSION: 23.5.26
   WABT_VERSION: 1.0.36