zig fmt: wrong output for empty tagged containers with document comments

[gooncreeper]

Zig Version

0.15.0-dev.451+a843be44a

Steps to Reproduce and Observed Behavior

Run zig fmt on the following code,

const A = union(enum(u32)) {
    //! Hello World!
};

It incorrectly formats it to

const A = union(enum(u32)) {
    //! Hello World!
//! Hello World!

This applies to packed struct(T), union(T), union(enum(T)), and enum(T)

This happens since Ast.lastToken assumes that when these have no members, the only following tokens are ){}. This also means the bug may also observable in other parts of the compiler, but it is easiest to observe with zig fmt.

Expected Behavior

No change.