Can't write comments in refactoring tests

[jackfirth]

This ought to be possible:

#lang resyntax/testing/refactoring-test

header:
- #lang racket/base

; See issue #12345, where this caused a bug in Resyntax because of x, y, and z.
test: "should not touch foo"
--------------------
(foo 42)
--------------------

But the lexer for the refactoring test language doesn't currently allow comments. The closest we can get is by putting the comments inside the test case code block, but that can cause other problems since refactoring tests check that Resyntax preserves the comments in the code blocks being refactored.