Fix picklecommon for Python 3.14 and older

Author: vstinner

Lib/test/picklecommon.py

@@ -252,9 +252,6 @@ class MyList(list):
 class MyDict(dict):
     sample = {"a": 1, "b": 2}
 
-class MyFrozenDict(dict):
-    sample = frozendict({"a": 1, "b": 2})
-
 class MySet(set):
     sample = {"a", "b"}
 
@@ -264,7 +261,18 @@ class MyFrozenSet(frozenset):
 myclasses = [MyInt, MyLong, MyFloat,
              MyComplex,
              MyStr, MyUnicode,
-             MyTuple, MyList, MyDict, MyFrozenDict, MySet, MyFrozenSet]
+             MyTuple, MyList, MyDict, MySet, MyFrozenSet]
+
+try:
+    frozendict
+except NameError:
+    # Python 3.14 and older
+    pass
+else:
+    class MyFrozenDict(dict):
+        sample = frozendict({"a": 1, "b": 2})
+    myclasses.append(MyFrozenDict)
+
 
 # For test_newobj_overridden_new
 class MyIntWithNew(int):