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
version_suffix: str,
                               package_dependencies: Iterable[str],
                               extras: Dict[str, List[str]],
                               backport_packages: bool) -> None:
    """
    The main setup method for package.
    :param provider_package_id: id of the provider package
    :param version_suffix: version suffix to be added to the release version (for example rc1)
    :param package_dependencies: dependencies of the package
    :param extras: extras of the package
    :param backport_packages: whether to prepare regular (False) or backport (True) packages
    """
    setup.write_version()
    provider_package_name = get_pip_package_name(provider_package_id, backport_packages=backport_packages)
    package_name = f'{provider_package_name}'
    package_prefix = f'airflow.providers.{provider_package_id}'
    found_packages = find_packages()
    found_packages = [package for package in found_packages if package.startswith(package_prefix)]