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:
        airflow_dependency = 'apache-airflow~=1.10' if provider_package_id != 'cncf.kubernetes' \
            else 'apache-airflow>=1.10.12, <2.0.0'
    else:
        airflow_dependency = 'apache-airflow>=2.0.0'
    install_requires = [
        airflow_dependency
    ]
    install_requires.extend(package_dependencies)
    description_prefix = 'Back-ported' if backport_packages else 'Regular'
    description_suffix = 'for Airflow 1.10.*' if backport_packages else 'for Airflow 2+'
    setuptools_setup(
        name=package_name,
        description=f'{description_prefix} {package_prefix}.* package {description_suffix}',
        long_description=get_long_description(provider_package_id, backport_packages=backport_packages),
        long_description_content_type='text/markdown',
        license='Apache License 2.0',
        version=get_package_release_version(
            provider_package_id=provider_package_id,
            backport_packages=backport_packages,
            version_suffix=version_suffix),
        packages=found_packages,
        zip_safe=False,
        install_requires=install_requires,
        extras_require=extras,
        classifiers=[
            'Development Status :: 5 - Production/Stable',
            'Environment :: Console',
            'Intended Audience :: Developers',
            'Intended Audience :: System Administrators',