[llvm] [mlir] Fix nested codeowners for vector dialect (PR #115473)

[Kunwar Grover via llvm-commits]

Groverkss wrote:

> 1. Do you have a link documenting how CODEOWNERS works? It would be good to add that in the summary.

Yes, it's in github docs: https://github.com/llvm/llvm-project/pull/118208 I can raise a new pr to add that into the CODEOWNERS summary

> 2. Shall we keep the list of reviewers in alphabetical order?

Sure.

https://github.com/llvm/llvm-project/pull/115473