**What happened**:

`pandas-gbq` released version [0.15.0](https://github.com/pydata/pandas-gbq/releases/tag/0.15.0) which broke `apache-airflow-backport-providers-google==2020.11.23`

```
../lib/python3.7/site-packages/airflow/providers/google/cloud/hooks/bigquery.py:49: in <module>
    from pandas_gbq.gbq import (
E   ImportError: cannot import name '_check_google_client_version' from 'pandas_gbq.gbq' (/usr/local/lib/python3.7/site-packages/pandas_gbq/gbq.py)
```

The fix is to pin `pandas-gpq==0.14.1`.
setup.py
'apache.hdfs',
    'apache.hive',
    'apache.pinot',
    'cloudant',
    'exasol',
    'microsoft.mssql',
    'mongo',
    'mysql',
    'neo4j',
    'postgres',
    'presto',
    'vertica',
]
all_dbs = list({req for db_provider in ALL_DB_PROVIDERS for req in PROVIDERS_REQUIREMENTS[db_provider]})
_all_requirements = list({req for extras_reqs in EXTRAS_REQUIREMENTS.values() for req in extras_reqs})
EXTRAS_REQUIREMENTS["all"] = _all_requirements
EXTRAS_REQUIREMENTS["all_dbs"] = all_dbs
devel_all = list(set(_all_requirements + doc + devel_minreq + devel_hadoop))
PACKAGES_EXCLUDED_FOR_ALL = []
PACKAGES_EXCLUDED_FOR_ALL.extend(
    [
        'snakebite',
    ]
)
#
#
PACKAGES_EXCLUDED_FOR_CI = [
    'apache-beam',
]
def is_package_excluded(package: str, exclusion_list: List[str]):