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
imported_classes: List[str], backport_packages: bool) -> Tuple[int, int]:
    """
    Updates release notes (BACKPORT_README.md/README.md) for the package. returns Tuple of total number
    of entities and badly named entities.
    :param provider_package_id: id of the package
    :param current_release_version: release version
    :param imported_classes - entities that have been imported from providers
    :param backport_packages: whether to prepare regular (False) or backport (True) packages
    :return: Tuple of total/bad number of entities
    """
    full_package_name = f"airflow.providers.{provider_package_id}"
    provider_package_path = get_package_path(provider_package_id)
    entity_summaries = get_package_class_summary(full_package_name, imported_classes)
    past_releases = get_all_releases(provider_package_path=provider_package_path,
                                     backport_packages=backport_packages)
    current_release_version, previous_release = check_if_release_version_ok(
        past_releases, current_release_version, backport_packages)
    cross_providers_dependencies = \
        get_cross_provider_dependent_packages(provider_package_id=provider_package_id)
    previous_release = get_previous_release_info(previous_release_version=previous_release,
                                                 past_releases=past_releases,
                                                 current_release_version=current_release_version)
    git_cmd = get_git_command(previous_release)
    changes = subprocess.check_output(git_cmd, cwd=provider_package_path, universal_newlines=True)
    changes_table = convert_git_changes_to_table(
        changes,
        base_url="https://github.com/apache/airflow/commit/")
    pip_requirements_table = convert_pip_requirements_to_table(PROVIDERS_REQUIREMENTS[provider_package_id])