rust-filepatterns: fix type of warnings tuple to (bytes, bytes) Otherwise warn() in match.py would fail if the warning contains non-ASCII character. We might want to add a thin ByteString wrapper around Vec<u8> to implement ToPyObject<ObjectType = PyBytes>, but I'm not sure.

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_CN
  checking for parse errors