AttributeError on Debug Run with PyTest

Start by reproducing the pytest run with debugpy 1.8.16 and comparing it with 1.8.15. Read debugpy/adapter/main.py, debugpy/public_api.py, and the bundled dataclasses.py around the reported _ClassVar lookup; done means collection completes and wait_for_client() no longer times out under the reported environment.

Environment data

• debugpy version: 1.8.16
• OS and version: Ubuntu 20.04.6 LTS
• Python version: 3.12.3
• Using VS Code or Visual Studio: VS Code

Actual behavior

collecting ... Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/__main__.py", line 229, in <module>
    __import__("debugpy")
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/../../debugpy/__init__.py", line 36, in <module>
    from debugpy.public_api import *  # noqa
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/../../debugpy/public_api.py", line 25, in <module>
    @dataclasses.dataclass(frozen=True)
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/../../dataclasses.py", line 950, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/../../dataclasses.py", line 800, in _process_class
    cls_fields = [_get_field(cls, name, type)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/../../dataclasses.py", line 659, in _get_field
    if (_is_classvar(a_type, typing)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jp/.pyenv/versions/3.12.3/envs/dev/lib/python3.12/site-packages/debugpy/adapter/../../dataclasses.py", line 550, in _is_classvar
    return type(a_type) is typing._ClassVar
                           ^^^^^^^^^^^^^^^^
AttributeError: module 'typing' has no attribute '_ClassVar'. Did you mean: 'ClassVar'?

Expected behavior

PyTest collects test(s), macro in code waits for connection from VS Code, debugging proceeds.

Steps to reproduce:

Use debugpy version 1.8.16 (downgrading to 1.8.15 fixed the problem), run a pytest for code that contains the debugpy code macro as I have below and wait a few seconds. The traceback will be reported and the wait_for_client() call will time out.

import debugpy
debugpy.listen(5679)
debugpy.wait_for_client()