[llvm] [ci] Use different emoji for Linux and Windows job titles on GitHub (PR #142101)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

Given it's markdown, I'm guessing we could probably get `<img>` tags to display what we want. Probably more hassle than it's worth though. This is definitely the most reasonable path forward currently.

Thanks for the patch!

https://github.com/llvm/llvm-project/pull/142101