Fix link to is-deeply()

doc/Type/Test.pod6

@@ -164,7 +164,7 @@ B<NOTE:> the C<eq> operator stringifies its operands, which means C<is()> is not
 a good function for testing more complex things, such as lists: C<is (1, (2,
 (3,))), [1, 2, 3]> passes the test, even though the operands are vastly
 different. For those cases, use
-L«C<is-deeply> routine|/language/testing#index-entry-is-deeply-is-deeply($value,_$expected,_$description?)»
+L«C<is-deeply> routine|#sub_is-deeply»
 
 =for code :preamble<use Test;>
     my $pdf-document; sub factorial($x) { ... }; ...;