Fix the use of adaptive-fill-regexp in treesit indent preset

Fix the use of adaptive-fill-regexp in treesit indent preset

* lisp/treesit.el (treesit-simple-indent-presets):
adaptive-fill-regexp don't have a capture group (the group in the
default value is supposed to be a non-capture group), so don't use the
group. Also, in the second diff hunk, replace looking-at with
looking-at-p so it doesn't override match data that we use later.