Parse error in Nickel files with wildcard type annotations

[matthew-healy]

Describe the bug

Trying to format the following file with Topiary:

(let { a : { b : Number } = { b }} = { a = { b = "no" }} in
b) : _

results in this error:

[2023-05-26T09:12:17Z ERROR topiary] Parsing error between line 2, column 4 and line 2, column 7

Expected behavior

This is valid Nickel, so it should parse (& format) correctly.

[vkleen]

I think this is a bug in the tree-sitter grammar; (fun x => x) : _ produces a parse error without topiary being involved.