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
'CloudTextToSpeechSynthesizeOperator',
            'CloudSpeechToTextRecognizeSpeechOperator',
        }
    ), EntityType.Sensors: find_all_entities(
        imported_classes=imported_classes,
        base_package=full_package_name,
        sub_package_pattern_match=r".*\.sensors\..*",
        ancestor_match=BaseSensorOperator,
        expected_class_name_pattern=SENSORS_PATTERN,
        unexpected_class_name_patterns=ALL_PATTERNS - {OPERATORS_PATTERN, SENSORS_PATTERN}
    ), EntityType.Hooks: find_all_entities(
        imported_classes=imported_classes,
        base_package=full_package_name,
        sub_package_pattern_match=r".*\.hooks\..*",
        ancestor_match=BaseHook,
        expected_class_name_pattern=HOOKS_PATTERN,
        unexpected_class_name_patterns=ALL_PATTERNS - {HOOKS_PATTERN}
    ), EntityType.Secrets: find_all_entities(
        imported_classes=imported_classes,
        sub_package_pattern_match=r".*\.secrets\..*",
        base_package=full_package_name,
        ancestor_match=BaseSecretsBackend,
        expected_class_name_pattern=SECRETS_PATTERN,
        unexpected_class_name_patterns=ALL_PATTERNS - {SECRETS_PATTERN},
    ), EntityType.Transfers: find_all_entities(
        imported_classes=imported_classes,
        base_package=full_package_name,
        sub_package_pattern_match=r".*\.transfers\..*",
        ancestor_match=BaseOperator,
        expected_class_name_pattern=TRANSFERS_PATTERN,