986a805c added dist/IO/t/io_utf8argv.t which creates a utf-8 test file
from raw bytes. When PERL_UNICODE was set the bytes were encoded as
utf-8, so producing a double-encode file.
Create the file with :raw to avoid that.
plan(tests => 2);
-open my $fh, ">", 'io_utf8argv';
+open my $fh, ">:raw", 'io_utf8argv';
print $fh
"\xce\x9c\xe1\xbd\xb7\xce\xb1\x20\xcf\x80\xe1\xbd\xb1\xcf\x80\xce".
"\xb9\xce\xb1\x2c\x20\xce\xbc\xe1\xbd\xb0\x20\xcf\x80\xce\xbf\xce".