support for gcr-4

[decathorpe]

GNOME 43 will be released with a new major version of gcr (gcr-4 vs. gcr-3).

At least in Fedora 37, those two will be packaged separately and installable in parallel, but gcr-3 will not be supported forever. capnet-assist will, at some point, need to add support for, or be ported to, gcr-4.

More context for this change is available on the Fedora development mailing list.

[davidmhewitt]

We'd actually need to provide our own widget here because Gcr no longer ships UI widgets in gcr-4, which is the only thing we use it for here:

https://gitlab.gnome.org/GNOME/gcr/-/blob/master/NEWS#L6

[danirabbit]

Fixed in #113 :)