The dependencies in Alphas are currently >= 2.0.0 and should be >=2.0.0a0 in order to work with Alphas in cases which are not PEP 440-compliant.

According to https://www.python.org/dev/peps/pep-0440/, >= 2.0.0 should also work with alpha/beta releases (a1/a2) but in some cases it does not (https://apache-airflow.slack.com/archives/C0146STM600/p1602774750041800) 

Changing to ">=2.0.0a0" should help.
provider_packages/setup_provider_packages.py
'License :: OSI Approved :: Apache Software License',
            'Programming Language :: Python :: 3.6',
            'Programming Language :: Python :: 3.7',
            'Programming Language :: Python :: 3.8',
            'Topic :: System :: Monitoring',
        ],
        setup_requires=[
            'bowler',
            'docutils',
            'gitpython',
            'setuptools',
            'wheel',
        ],
        python_requires='>=3.6',
    )
def find_package_extras(package: str, backport_packages: bool) -> Dict[str, List[str]]:
    """
    Finds extras for the package specified.
    :param package: id of the package
    :param backport_packages: whether to prepare regular (False) or backport (True) packages
    """
    if package == 'providers':
        return {}
    with open(DEPENDENCIES_JSON_FILE, "rt") as dependencies_file:
        cross_provider_dependencies: Dict[str, List[str]] = json.load(dependencies_file)
    extras_dict = {module: [get_pip_package_name(module, backport_packages=backport_packages)]
                   for module in cross_provider_dependencies[package]} \
        if cross_provider_dependencies.get(package) else {}
    return extras_dict
def get_provider_packages():