Fix compatibility with QMYSQL driver after 74aed954

Summary:
QPSQL requires the table name passed to QSqlDatabase::record() to be lowercase
since Qt 5.13, but doing that breaks QMYSQL, so only adjust the name when
using QPSQL.

CCBUG: 409234

Reviewers: #kde_pim, vkrause

Reviewed By: #kde_pim, vkrause

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D22677