tree-sitter-yaml definitely exists[1]. Presumably nobody has packaged it for Arch yet; that seems like a thing you could contribute.

[1]: https://github.com/tree-sitter-grammars/tree-sitter-yaml

It's in the AUR (aur/tree-sitter-yaml), a community-driven repository of Arch Linux packages. Not yet official.

Since it comes from `tree-sitter-grammars/tree-sitter-yaml`, it may be quick to integrate the official repo.