Tests: added to CustomClass immutable object that would trigger a setattr() exception

tests/test_persistence.py

@@ -18,6 +18,7 @@
 # along with this program.  If not, see [http://www.gnu.org/licenses/].
 import gzip
 import signal
+import uuid
 from threading import Lock
 
 from telegram.ext.callbackdatacache import CallbackDataCache
@@ -582,6 +583,7 @@ class TestBasePersistence:
                 self.frozenset_ = frozenset(self.list_)
                 self.dict_ = {item: item for item in self.list_}
                 self.defaultdict_ = defaultdict(dict, self.dict_)
+                self.uuid_ = uuid.uuid4()
 
             @staticmethod
             def replace_bot():