Clarify is-deeply bug-by-design affects only Seq:D

For Seq type objects it used to crash, but now fixed[^1] and
tested[2], to pass them through non-buggy path in is-deeply.

[1] rakudo/rakudo@f3f99b3ac4
[2] Raku/roast@3ea879737b

Author: zoffixznet

doc/Language/testing.pod6

@@ -416,7 +416,7 @@ is-deeply count-chars('fleece'), %expected, 'count-chars works on "fleece"';
 =end code
 
 B<Note:> for L<historical
-reasons|https://github.com/rakudo/rakudo/commit/096bc17cd5>, L<Seq> arguments
+reasons|https://github.com/rakudo/rakudo/commit/096bc17cd5>, L<Seq:D|/type/Seq> arguments
 to C<is-deeply> get converted to L<Lists|/type/List>. If you want to ensure
 strict C<Seq> comparisons, use
 L«C<cmp-ok $got, 'eqv', $expected, $desc>|/language/testing#index-entry-cmp-ok-cmp-ok%28%24value%2C_%24comparison%2C_%24expected%2C_%24description%3F%29> instead.