Fix statements being autocommitted using implicit autocommit

[jpvanhal]

Fix the following sqlalchemy.exc.RemovedIn20Warning warnings:

sqlalchemy.exc.RemovedIn20Warning: The current statement is being
autocommitted using implicit autocommit, which will be removed in
SQLAlchemy 2.0. Use the .begin() method of Engine or Connection in
order to use an explicit transaction for DML and DDL statements.
(Background on SQLAlchemy 2.0 at: https://sqlalche.me/e/b8d9)