Improve example with explicit state

Using state in `where` clause is UB and should not be shown in the docs.

doc/Language/variables.pod6

@@ -714,9 +714,9 @@ itself, not the expression that may contain an initializer. If the
 initializer has to be called exactly once, the C<state> declarator has to be
 provided.
 
-=begin code :skip-test
-subset DynInt where $ = ::('Int'); # the initializer will be called for each type check
-subset DynInt where state $ = ::('Int'); # the initializer is called once, this is a proper cache
+=begin code
+for ^3 {       $ = .say } # OUTPUT: «0␤1␤2␤»
+for ^3 { state $ = .say } # OUTPUT: «0␤»
 =end code
 
 =head3 The C<@> variable