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
'Environment :: Web Environment',
            'Intended Audience :: Developers',
            'Intended Audience :: System Administrators',
            'License :: OSI Approved :: Apache Software License',
            'Programming Language :: Python :: 3.6',
            'Programming Language :: Python :: 3.7',
            'Programming Language :: Python :: 3.8',
            'Topic :: System :: Monitoring',
        ],
        author='Apache Software Foundation',
        author_email='dev@airflow.apache.org',
        url='http://airflow.apache.org/',
        download_url=(
            'https://archive.apache.org/dist/airflow/' + version),
        cmdclass={
            'extra_clean': CleanCommand,
            'compile_assets': CompileAssets,
            'list_extras': ListExtras,
        },
        test_suite='setup.airflow_test_suite',
        python_requires='~=3.6',
        project_urls={
            'Documentation': 'https://airflow.apache.org/docs/',
            'Bug Tracker': 'https://github.com/apache/airflow/issues',
            'Source Code': 'https://github.com/apache/airflow',
        },
    )
if __name__ == "__main__":
    do_setup()