Cap the version of mysqlclient on Python 2.7.
Review Request #11909 — Created Jan. 7, 2022 and submitted — Latest diff uploaded
mysqlclient2.0+ dropped support for Python 2.7. In order to maintain
compatibility without issues, theReviewBoard[mysql]dependency now
caps the version at < 1.5 (as a precaution) on Python 2.7.
Tested installing the dependency on Python 2.7 and all 3.6+.