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

[via llvm-commits]

forking-renovate[bot] wrote:

### Renovate Ignore Notification

Because you closed this PR without merging, Renovate will ignore this update. You will not get PRs for *any* future `6.x` releases. But if you manually upgrade to `6.x` then Renovate will re-enable `minor` and `patch` updates automatically.

If you accidentally closed this PR, or if you changed your mind: rename this PR to get a fresh replacement PR.

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