Similar, although not the same, situation here.
Since both the a2enmod and a2dismod scripts follow the same logic:
if ( module to enable/disable is cgi && MPM is threaded (worker) )
then cgid is enabled/disabled instead
I think, we should be disabling cgi module *BEFORE* apache2-mpm-worker is installed.
I failed to do so, therefore disabled mod cgi manually:
$ sudo rm /etc/apache2/mods-enabled/cgi.load
Denisa