chore(deps): update dependency pandas-gbq to v0.15.0 (GoogleCloudPlatform#5602)

* chore(deps): update dependency pandas-gbq to v0.15.0

* add python version check for pandas-gbq

* fix typo

Co-authored-by: Leah Cole <[email protected]>

Author: renovate-bot

bigquery/pandas-gbq-migration/requirements.txt

@@ -2,6 +2,7 @@ google-cloud-bigquery==2.13.1
 google-cloud-bigquery-storage==2.3.0
 pandas==1.1.5; python_version < '3.7'
 pandas==1.2.0; python_version > '3.6'
-pandas-gbq==0.14.1
+pandas-gbq==0.15.0; python_version > '3.6'
+pandas-gbq==0.14.1; python_version < '3.7'
 pyarrow==3.0.0
 grpcio==1.36.1