/etc/php/7.0/mods-available/gmagick.ini is in php-gmagick 2.0.4~rc1+1.1.7~rc3-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | ; configuration for php imagick module
extension=gmagick.so
|