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
readme_template_name = "BACKPORT_PROVIDERS_README" if backport_packages else "PROVIDERS_README"
    readme += render_template(template_name=readme_template_name, context=context)
    classes_template_name = "BACKPORT_PROVIDERS_CLASSES" if backport_packages else "PROVIDERS_CLASSES"
    readme += render_template(template_name=classes_template_name, context=context)
    for a_release in all_releases:
        readme += a_release.content
    readme_file_path = os.path.join(provider_package_path,
                                    "BACKPORT_README.md" if backport_packages else "README.md")
    old_text = ""
    if os.path.isfile(readme_file_path):
        with open(readme_file_path, "rt") as readme_file_read:
            old_text = readme_file_read.read()
    if old_text != readme:
        _, temp_file_path = tempfile.mkstemp(".md")
        try:
            if os.path.isfile(readme_file_path):
                copyfile(readme_file_path, temp_file_path)
            with open(readme_file_path, "wt") as readme_file:
                readme_file.write(readme)
            print()
            print(f"Generated {readme_file_path} file for the {provider_package_id} provider")
            print()
            if old_text != "":
                subprocess.call(["diff", "--color=always", temp_file_path, readme_file_path])
        finally:
            os.remove(temp_file_path)
    total, bad = check_if_classes_are_properly_named(entity_summaries)
    bad = bad + sum([len(entity_summary.wrong_entities) for entity_summary in entity_summaries.values()])
    if bad != 0:
        print()