test: tweak in alignment involving unprintable characters
This looks like a bug fix since the caret is now pointing right at the
position of the unprintable character. I'm not sure if this is a result
of an improvement via the `annotate-snippets` upgrade, or because of
more accurate tracking of annotation ranges even after unprintable
characters are replaced. I'm tempted to say the former since in theory
the offsets were never wrong before because they were codepoint offsets.
Regardless, this looks like an improvement.
