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
"""Set default values for options."""
    def finalize_options(self):
        """Set final values for options."""
    def run(self):  
        """Run command to remove temporary files and directories."""
        os.chdir(dirname(__file__))
        os.system('rm -vrf ./build ./dist ./*.pyc ./*.tgz ./*.egg-info')
sys.path.insert(0, SOURCE_DIR_PATH)
import setup  
DEPENDENCIES_JSON_FILE = os.path.join(PROVIDERS_PATH, "dependencies.json")
MOVED_ENTITIES: Dict[EntityType, Dict[str, str]] = {
    EntityType.Operators: {value[0]: value[1] for value in tests.deprecated_classes.OPERATORS},
    EntityType.Sensors: {value[0]: value[1] for value in tests.deprecated_classes.SENSORS},
    EntityType.Hooks: {value[0]: value[1] for value in tests.deprecated_classes.HOOKS},
    EntityType.Secrets: {value[0]: value[1] for value in tests.deprecated_classes.SECRETS},
    EntityType.Transfers: {value[0]: value[1] for value in tests.deprecated_classes.TRANSFERS},
}
def get_pip_package_name(provider_package_id: str, backport_packages: bool) -> str:
    """
    Returns PIP package name for the package id.
    :param provider_package_id: id of the package
    :param backport_packages: whether to prepare regular (False) or backport (True) packages
    :return: the name of pip package
    """
    return ("apache-airflow-backport-providers-" if backport_packages else "apache-airflow-providers-") \
        + provider_package_id.replace(".", "-")
def get_long_description(provider_package_id: str, backport_packages: bool) -> str: