Don't show the welcome dialog in classic mode
One of the changes in GNOME 40 is a new welcome dialog which is shown on first run. The dialog invites the user to launch gnome-tour.
The dialog is problematic under classic mode - the content in gnome-tour isn't relevant to classic mode, and classic mode users don't really need onboarding anyway.
It would therefore be better if we didn't show this dialog in the classic mode case.