[llvm] [Github] Fetch all commits in PR for code formatting checks (PR #69766)

[Tobias Hieta via llvm-commits]

tru wrote:

Nicely done! It looks like a good approach. If I understand the spare checkout correctly it's only to get the scripts to run. Can't we fetch these files with curl instead of a sparse checkout? Should be faster and it's what we do in other places. 

https://github.com/llvm/llvm-project/pull/69766