build: Fix building with -Werror=format-security
Otherwise build fails with:
../src/gui/gtd-window.c: In function 'error_message_notification_secondary_action':
../src/gui/gtd-window.c:145:35: error: format not a string literal and no format arguments [-Werror=format-security]
145 | data->secondary_text);
| ^~~~
cc1: some warnings being treated as errors
See also https://gitlab.gnome.org/GNOME/gnome-text-editor/-/blob/43.alpha0/src/editor-page.c#L1077
Thanks for reviewing!