Fix "diag "foo"|"bar"

We allow junctions to be specified in e.g. "is", but if they fail, they
used to bomb on the "diag" being done.  This fixes the bombing.   This is
spectests clean.

Inspired by Text::CSV ecosystem fallout, following hash randomization changes
needing tests to be fixed.

lib/Test.pm6

@@ -423,14 +423,14 @@ multi sub subtest(&subtests, $desc = '') is export {
     proclaim($status,$desc) or ($die_on_fail and die-on-fail);
 }
 
-sub diag(Mu $message) is export {
+sub diag($message) is export {
     # Always send user-triggered diagnostics to STDERR. This prevents
     # cases of confusion of where diag() has to send its ouput when
     # we are in the middle of TODO tests
     _diag $message, :force-stderr;
 }
 
-sub _diag(Mu $message, :$force-stderr) {
+sub _diag($message, :$force-stderr) {
     _init_io() unless $output;
     my $is_todo = !$force-stderr
         && ($subtest_todo_reason || $num_of_tests_run <= $todo_upto_test_num);