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
version=version,
        packages=find_packages(
            include=['airflow*'],
            exclude=exclude_patterns),
        package_data={
            'airflow': ['py.typed'],
            '': ['airflow/alembic.ini', "airflow/git_version", "*.ipynb",
                 "airflow/providers/cncf/kubernetes/example_dags/*.yaml"],
            'airflow.api_connexion.openapi': ['*.yaml'],
            'airflow.serialization': ["*.json"],
        },
        include_package_data=True,
        zip_safe=False,
        entry_points={
            "console_scripts": [
                "airflow = airflow.__main__:main",
            ],
        },
        install_requires=INSTALL_REQUIREMENTS,
        setup_requires=[
            'bowler',
            'docutils',
            'gitpython',
            'setuptools',
            'wheel',
        ],
        extras_require=EXTRAS_REQUIREMENTS,
        classifiers=[
            'Development Status :: 5 - Production/Stable',
            'Environment :: Console',