Error when upgrading to 2.2.1

First of all, great work with this plugin.. love it! :)

I got an error in a dockerized CI (Linux) and on my Windows-WSL machine when upgrading to 2.2.1 (from 2.2.0)

INTERNALERROR> def worker_internal_error(self, node, formatted_error):
INTERNALERROR>         """
INTERNALERROR>         pytest_internalerror() was called on the worker.
INTERNALERROR>
INTERNALERROR>         pytest_internalerror() arguments are an excinfo and an excrepr, which can't
INTERNALERROR>         be serialized, so we go with a poor man's solution of raising an exception
INTERNALERROR>         here ourselves using the formatted message.
INTERNALERROR>         """
INTERNALERROR>         self._active_nodes.remove(node)
INTERNALERROR>         try:
INTERNALERROR> >           assert False, formatted_error
INTERNALERROR> E           AssertionError: Traceback (most recent call last):
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/_pytest/main.py", line 191, in wrap_session
INTERNALERROR> E                 session.exitstatus = doit(config, session) or 0
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/_pytest/main.py", line 246, in _main
INTERNALERROR> E                 config.hook.pytest_collection(session=session)
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
INTERNALERROR> E                 return self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
INTERNALERROR> E                 return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
INTERNALERROR> E                 self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/callers.py", line 208, in _multicall
INTERNALERROR> E                 return outcome.get_result()
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/callers.py", line 80, in get_result
INTERNALERROR> E                 raise ex[1].with_traceback(ex[2])
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/callers.py", line 187, in _multicall
INTERNALERROR> E                 res = hook_impl.function(*args)
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/_pytest/main.py", line 257, in pytest_collection
INTERNALERROR> E                 return session.perform_collect()
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/_pytest/main.py", line 453, in perform_collect
INTERNALERROR> E                 self.config.pluginmanager.check_pending()
INTERNALERROR> E               File "/home/emil/.local/lib/python3.8/site-packages/pluggy/manager.py", line 274, in check_pending
INTERNALERROR> E                 raise PluginValidationError(
INTERNALERROR> E             pluggy.manager.PluginValidationError: unknown hook 'pytest_warning_recorded' in plugin <__channelexec__.WorkerInteractor object at 0x7f79f94f5b80>
INTERNALERROR> E           assert False

I fixed it by downgrading to 2.2.0 again. Running pytest 6.2.2.

Just comment if you need any more information! :)

Start by reproducing the reported upgrade from pytest-xdist 2.2.0 to 2.2.1 with pytest 6.2.2 in the Docker or Windows-WSL environments described. Investigate the collection-time PluginValidationError for the unknown pytest_warning_recorded hook; done means pytest collection and distributed tests run without this internal error.