New parser: A variable name starting with "as" is okay as the 1st variable in a function but not the 2nd.

The following code compiles fine with the Haskell-based compiler:

module Main exposing (good, bad)

import Array

good : Int -> Int -> Int
good as_ bs =
    as_ + bs

bad : Int -> Int -> Int -> Int
bad x as_ bs =
    x + as_ + bs

as seen in:

% gren make Main                                                   
Success! Compiled 1 module.

But the new compiler-common parser thinks the "as" in "as_" (as the 2nd argument in the "bad" function) is a reserved keyword and doesn't like the "_" after it:

% ~/prj/gren-format/gren-format/gren-format.sh --show src/Main.gren
-- FAILED TO PARSE ----------------------------------------------- src/Main.gren

 8| 
 9| bad : Int -> Int -> Int -> Int
10| bad x as_ bs =
            ^
11|     x + as_ + bs
12| 

Invalid character in variable name

But it has no problem with the "as_" in the "good" function where it is the 1st argument.

This file can be found in the 2026-06-30-trailing_underscore directory in this repo: https://github.com/gilramir/gren-bug-reports

Reproduce the parser failure with gren-format.sh using src/Main.gren from the 2026-06-30-trailing_underscore directory. Start by tracing how variable names are parsed in the compiler-common parser, then verify that as_ is accepted in both argument positions while the supplied example still parses successfully.