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
"""
    Converts the class name to URL that the class can be reached
    :param base_url: base URL to use
    :param class_name: name of the class
    :return: URL to the class
    """
    return base_url + os.path.sep.join(class_name.split(".")[:-1]) + ".py"
def get_class_code_link(base_package: str, class_name: str, git_tag: str) -> str:
    """
    Provides markdown link for the class passed as parameter.
    :param base_package: base package to strip from most names
    :param class_name: name of the class
    :param git_tag: tag to use for the URL link
    :return: URL to the class
    """
    url_prefix = f'https://github.com/apache/airflow/blob/{git_tag}/'
    return f'[{strip_package_from_class(base_package, class_name)}]' \
           f'({convert_class_name_to_url(url_prefix, class_name)})'
def print_wrong_naming(entity_type: EntityType, wrong_classes: List[Tuple[type, str]]):
    """
    Prints wrong entities of a given entity type if there are any
    :param entity_type: type of the class to print
    :param wrong_classes: list of wrong entities
    """
    if wrong_classes:
        print(f"\nThere are wrongly named entities of type {entity_type}:\n", file=sys.stderr)
        for entity_type, message in wrong_classes:
            print(f"{entity_type}: {message}", file=sys.stderr)
def get_package_class_summary(full_package_name: str, imported_classes: List[str]) \