[llvm] [github] Add ClangIR to new-prs-labeler.yml (PR #86088)

[Tom Stellard via llvm-commits]

tstellar wrote:

> No needs for team to label PRs. However, there needs to be a team for notifications to work. Maybe Tom/Tobias can help with teams creation.
> 
> The name of the label/team must match and it needs to be all lowercase afaik.

Uppercase labels are OK. I've added the team now.

https://github.com/llvm/llvm-project/pull/86088