[llvm] [llvm][docs] Reorder Stacked PR approaches in GitHub.rst (PR #138126)

[Andrzej Warzyński via llvm-commits]

https://github.com/banach-space approved this pull request.

LGTM, thanks!

Perhaps wait one more day before landing, just in case  @boomanaiden154 has further comments (all other active reviewers have already approved).

https://github.com/llvm/llvm-project/pull/138126