Adapt tests to new Set|Bag|Mix.new() behaviour

As implemented in aab2b98

Author: lizmat

S02-types/bag.t

@@ -539,7 +539,7 @@ subtest '.hash does not cause keys to be stringified' => {
 }
 
 {
-    ok Bag.new =:= bag(), 'Bag.new returns the empty bag';
+    nok Bag.new =:= bag(), 'Bag.new returns a new empty bag';
     ok ().Bag  =:= bag(), '().Bag returns the empty bag';
 }
 

S02-types/mix.t

@@ -489,7 +489,7 @@ subtest '.hash does not cause keys to be stringified' => {
 }
 
 {
-    ok Mix.new =:= mix(), 'Mix.new returns the empty mix';
+    nok Mix.new =:= mix(), 'Mix.new returns a new empty mix';
     ok ().Mix  =:= mix(), '().Mix returns the empty mix';
 }
 

S02-types/set.t

@@ -475,7 +475,7 @@ subtest '.hash does not cause keys to be stringified' => {
 }
 
 {
-    ok Set.new =:= set(), 'Set.new returns the empty set';
+    nok Set.new =:= set(), 'Set.new returns a new empty set';
     ok ().Set  =:= set(), '().Set returns the empty set';
 }