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

[Andrzej Warzyński via llvm-commits]

https://github.com/banach-space commented:

Thanks for the fix!

1. Do you have a link documenting how CODEOWNERS works? It would be good to add that in the summary.
2. Shall we keep the list of reviewers in alphabetical order?

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