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
"""
    Returns source directory for providers (from the main airflow project).
    :return: the folder path
    """
    return os.path.join(get_source_airflow_folder(), "airflow", "providers")
def get_target_providers_folder() -> str:
    """
    Returns target directory for providers (in the provider_packages folder)
    :return: the folder path
    """
    return os.path.abspath(os.path.join(dirname(__file__), "airflow", "providers"))
def get_target_providers_package_folder(provider_package_id: str) -> str:
    """
    Returns target package folder based on package_id
    :return: the folder path
    """
    return os.path.join(get_target_providers_folder(), *provider_package_id.split("."))
class CleanCommand(Command):
    """
    Command to tidy up the project root.
    Registered as cmd class in setup() so it can be called with ``python setup.py extra_clean``.
    """
    description = "Tidy up the project root"
    user_options: List[str] = []
    def initialize_options(self):