The gnomeos-basic-ci component already has support for gobject-linter
and we only need to add a config file to make it run and show up as
part of a merge request's code quality check.
I set the property enum convention to "legacy", as that is the style
we currently use. Since this is only a matter of style, I do not see
the point in changing all (>40 occurrences) of that just because.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/799>
