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
"""
    In case expected_pattern is set, it checks if the package name matches the pattern.
    .
    :param the_class: imported class
    :param expected_pattern: the pattern that should match the package
    :return: true if the expected_pattern is None or the pattern matches the package
    """
    return expected_pattern is None or re.match(expected_pattern, the_class.__module__)
def find_all_entities(
        imported_classes: List[str],
        base_package: str,
        ancestor_match: Type,
        sub_package_pattern_match: str,
        expected_class_name_pattern: str,
        unexpected_class_name_patterns: Set[str],
        exclude_class_type: Type = None,
        false_positive_class_names: Optional[Set[str]] = None) -> VerifiedEntities:
    """
    Returns set of entities containing all subclasses in package specified.
    :param imported_classes: entities imported from providers
    :param base_package: base package name where to start looking for the entities
    :param sub_package_pattern_match: this string is expected to appear in the sub-package name
    :param ancestor_match: type of the object the method looks for
    :param expected_class_name_pattern: regexp of class name pattern to expect
    :param unexpected_class_name_patterns: set of regexp of class name pattern that are not expected
    :param exclude_class_type: exclude class of this type (Sensor are also Operators so
           they should be excluded from the list)
    :param false_positive_class_names: set of class names that are wrongly recognised as badly named