Update Devcontainer readme

Author: savannahostrowski

Tools/jit/README.md

@@ -54,7 +54,7 @@ choco install llvm --version=20.1.8
 ### Dev Containers
 
 If you are working on CPython in a [Codespaces instance](https://devguide.python.org/getting-started/setup-building/#using-codespaces), there's no 
-need to install LLVM as the Fedora 41 base image includes LLVM 19 out of the box.
+need to install LLVM as the Fedora 42 base image includes LLVM 20 out of the box.
 
 ## Building