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
cross_package_dependencies: List[str], base_url: str) -> str:
    """
    Converts cross-package dependencies to a markdown table
    :param cross_package_dependencies: list of cross-package dependencies
    :param base_url: base url to use for links
    :return: markdown-formatted table
    """
    from tabulate import tabulate
    headers = ["Dependent package", "Extra"]
    table_data = []
    for dependency in cross_package_dependencies:
        pip_package_name = f"apache-airflow-backport-providers-{dependency.replace('.','-')}"
        url_suffix = f"{dependency.replace('.','/')}"
        table_data.append((f"[{pip_package_name}]({base_url}{url_suffix})", dependency))
    return tabulate(table_data, headers=headers, tablefmt="pipe")
LICENCE = """<!--
 Licensed to the Apache Software Foundation (ASF) under one
 or more contributor license agreements.  See the NOTICE file