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 all providers that should be taken into account when preparing backports.
    For now we remove Papermill as it is deeply linked with Lineage in Airflow core and it won't work
    with lineage for Airflow 1.10 anyway.
    :return: list of providers that are considered for backport provider packages
    """
    excluded_providers = ["papermill"]
    return [prov for prov in PROVIDERS_REQUIREMENTS.keys() if prov not in excluded_providers]
def get_all_providers() -> List[str]: