[llvm] [Github] add spirv backend team (PR #66075)

[Tom Stellard via llvm-commits]

tstellar wrote:

Can you move these paths into [new-prs-labeler.yml](https://github.com/llvm/llvm-project/blob/main/.github/new-prs-labeler.yml).  We are no longer using the CODEOWNERS file for notifications.

https://github.com/llvm/llvm-project/pull/66075