flake8 and `importlib_metadata` 5.0 support

[tony]

flake8: 3.9.2
importlib-metadata: 5.0.0

how did you install flake8?

$ poetry install

unmodified output of flake8 --bug-report

{}

describe the problem

what I expected to happen

Normal usage

Traceback (most recent call last):
  File "/project/.venv/bin/flake8", line 8, in <module>
    sys.exit(main())
  File "/project/.venv/lib/python3.7/site-packages/flake8/main/cli.py", line 22, in main
    app.run(argv)
  File "/project/.venv/lib/python3.7/site-packages/flake8/main/application.py", line 363, in run
    self._run(argv)
  File "/project/.venv/lib/python3.7/site-packages/flake8/main/application.py", line 350, in _run
    self.initialize(argv)
  File "/project/.venv/lib/python3.7/site-packages/flake8/main/application.py", line 330, in initialize
    self.find_plugins(config_finder)
  File "/project/.venv/lib/python3.7/site-packages/flake8/main/application.py", line 153, in find_plugins
    self.check_plugins = plugin_manager.Checkers(local_plugins.extension)
  File "/project/.venv/lib/python3.7/site-packages/flake8/plugins/manager.py", line 357, in __init__
    self.namespace, local_plugins=local_plugins
  File "/project/.venv/lib/python3.7/site-packages/flake8/plugins/manager.py", line 238, in __init__
    self._load_entrypoint_plugins()
  File "/project/.venv/lib/python3.7/site-packages/flake8/plugins/manager.py", line 254, in _load_entrypoint_plugins
    eps = importlib_metadata.entry_points().get(self.namespace, ())
AttributeError: 'EntryPoints' object has no attribute 'get'

sample code

commands ran

$ flake8
...

[asottile]

please actually fill out the issue template and make sure to include your version info (hint hint)

[tony]

@asottile Sorry about that, I had it in edit in another tab and added it in.

[asottile]

you're 2 major versions of flake8 out of date

[tony]

Good point.

I came here through python/importlib_metadata#406, and use poetry, and it has a dependency of flake8 < 5: https://github.com/python/importlib_metadata/blob/v5.0.0/setup.cfg#L38

Will go back to them.