-p no:xdist in pytest.ini breaks various pytest plugins

[mgorny]

Implicitly disabling the xdist plugin via pytest.ini causes breakage if other plugins are installed that account for it, e.g. pytest-rerunfailures. At the same time, it doesn't seem to do anything meaningful — after all, xdist does not do anything unless you also specify -n ....

INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/_pytest/main.py", line 268, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/_pytest/main.py", line 321, in _main
INTERNALERROR>     config.hook.pytest_collection(session=session)
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/pluggy/_hooks.py", line 265, in __call__
INTERNALERROR>     return self._hookexec(self.name, self.get_hookimpls(), kwargs, firstresult)
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/pluggy/_manager.py", line 80, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/pluggy/_callers.py", line 60, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/pluggy/_result.py", line 60, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/pluggy/_callers.py", line 39, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/_pytest/main.py", line 332, in pytest_collection
INTERNALERROR>     session.perform_collect()
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/_pytest/main.py", line 659, in perform_collect
INTERNALERROR>     self.config.pluginmanager.check_pending()
INTERNALERROR>   File "/usr/lib/python3.10/site-packages/pluggy/_manager.py", line 262, in check_pending
INTERNALERROR>     raise PluginValidationError(
INTERNALERROR> pluggy._manager.PluginValidationError: unknown hook 'pytest_configure_node' in plugin <module 'pytest_rerunfailures' from '/usr/lib/python3.10/site-packages/pytest_rerunfailures.py'>