Avoid modifications if gin is not active

This allows the admin theme to change to something other than Gin without the need to disable Gin Moderation Sidebar.

Note that the toolbar might break in other ways if Gin Toolbar is left enabled, but that can be addressed by ✨ [gin_toolbar] Add _gin_toolbar_gin_is_active() check to all hook implementations Closed: won't fix .

Automatically closed - issue fixed for 2 weeks with no activity.