[llvm] [CI] Make monolithic-* scripts only run Github steps on Github (PR #152197)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Looks like I ran `spr land` on the wrong commit so this one landed without precommit review.

I'm going to leave this one in to avoid the churn of reverting/putting up another PR given this is small and does work. I'm happy to address postcommit comments if anyone has them. 

https://github.com/llvm/llvm-project/pull/152197