pythongh-89683: add tests for deepcopy on frozen dataclasses (pythongh-123098)

Co-authored-by: Bénédikt Tran <[email protected]>
Co-authored-by: Eric V. Smith <[email protected]>

# Conflicts:
#	Lib/test/test_dataclasses/__init__.py

Author: picnixz

Lib/test/test_dataclasses/__init__.py

@@ -16,8 +16,8 @@
 from unittest.mock import Mock
 from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol, DefaultDict
 from typing import get_type_hints
-from copy import deepcopy
 from collections import deque, OrderedDict, namedtuple, defaultdict
+from copy import deepcopy
 from functools import total_ordering
 
 import typing       # Needed for the string "typing.ClassVar[int]" to work as an annotation.