[llvm] [Github] Use our own issue labeler fork (PR #65900)

[via llvm-commits]

cor3ntin wrote:

> What is the difference between our fork and upstream?

- Only adds 'new issue' if no other label is added (https://github.com/llvm/llvm-project/issues/65701)
- No not add labels if labels were already set
- Only add `foo` if there are no `foo:bar` label being added (although, we don't use that yet)

https://github.com/llvm/llvm-project/pull/65900