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
if backport_packages:
        return f"apache-airflow-backport-providers-{provider_package_id.replace('.', '-')}"
    else:
        return f"apache-airflow-providers-{provider_package_id.replace('.', '-')}"
def update_release_notes_for_package(provider_package_id: str, current_release_version: str,