Update to conform to GLR. FROGGS++

roundrobin((); 1; 2..4; (5..7); <a b>) becomes
roundrobin([], [1], [2..4], [5..7], <a b>)

and

is(roundrobin([1..3]).elems, 1, 'roundrobin does not flatten array items');

just goes away, as that's not how these sorts of arguments work anymore.

S32-container/roundrobin.t

@@ -2,7 +2,7 @@ use v6;
 
 use Test;
 
-plan 5;
+plan 4;
 
 # L<S32::Containers/Container/"=item roundrobin">
 
@@ -21,10 +21,7 @@ is roundrobin(1).join, '1', 'roundrobin scalar identity';
 
 is(roundrobin(1..3).Str,  (1..3).Str, 'roundrobin list identity');
 
-#?rakudo todo 'over-flattening RT #124906'
-is(roundrobin([1..3]).elems, 1, 'roundrobin does not flatten array items');
-
-is(roundrobin((); 1; 2..4; (5..7); <a b>).join(' '),
+is(roundrobin([], [1], [2..4], [5..7], <a b>).join(' '),
    (1, 2, 5, 'a', 3, 6, 'b', 4, 7).join(' '), 'basic roundrobin');
 
 # vim: ft=perl6