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

[Nathan Gauër via llvm-commits]

Keenuts 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.

Right, matched the label name. Do you still need to create a new team first or shall we just merge this once approved?

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