Hi Clabin,
Make sure you have all the same PHP modules and packages installed for the newer PHP version.
dpkg -l | grep php should show you all installed PHP packages, and compare your old version with the newly installed version.
The error message says that it can’t find the PHP driver to connect to the DB.
Also make sure to restart your apache-php setup after successful installation, to enable the additional modules.
Edit: the gists are kind of useless, as long as we don’t know how they’ve been created. There can be a difference in version between the PHP version on the CLI and the one being used in Apache. Have a look at this other topic with a simliar problem: