Third-party repos: don't set the status if the user doesn't activate
If someone doesn't activate the third party repos, it's equivalent to them clicking through - it's a non-decision, rather than an explicit opt-out. It would therefore be correct not to change the third party repo setting.
This will result in the third party repo prompt being shown in Software, even if it isn't activated in initial setup (see gnome-software#2118 (closed)).