[llvm] Update actions/labeler action to v6 (PR #168300)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Needs to be done by reapplying b3d62645158cd6f463f2e1c878f6d63b9dc4b164 as this requires actual work, so closing.

https://github.com/llvm/llvm-project/pull/168300