The **attrs** and **cattrs** packages version is incompatible.
Check command:
`pip check --use-feature=2020-resolver`

Code file: https://github.com/apache/airflow/blob/master/setup.py
Commit hash: 9150330
Line number:
694: 'attrs~=19.3'
696: 'cattrs~=1.0'

It will caused the final installed **attrs** version is higher than 20.1.0.

Why this happen?
From the dependency setting of **cattrs**:
https://github.com/Tinche/cattrs/blob/master/setup.py
Commit hash: 2f401b9
Line number:
12: "attrs >= 20.1.0"

setup.py
#
#
#
"""Setup.py for the Airflow project."""
import io
import logging
import os
import subprocess
import sys
import unittest
from importlib import util
from os.path import dirname
from textwrap import wrap
from typing import Dict, Iterable, List
from setuptools import Command, find_packages, setup
logger = logging.getLogger(__name__)
spec = util.spec_from_file_location("airflow.version", os.path.join('airflow', 'version.py'))  
mod = util.module_from_spec(spec)
spec.loader.exec_module(mod)  
version = mod.version  
PY3 = sys.version_info[0] == 3
my_dir = dirname(__file__)
try:
    with io.open(os.path.join(my_dir, 'README.md'), encoding='utf-8') as f:
        long_description = f.read()
except FileNotFoundError:
    long_description = ''
def airflow_test_suite():