`camera_modification_in_fixed_update` doesn't catch all ways to add systems to `FixedUpdate`

[BD103]

There are lots of ways to add a system to a schedule, but camera_modification_in_fixed_update doesn't catch most of them. We currently do this:

bevy_cli/bevy_lint/src/lints/nursery/camera_modification_in_fixed_update.rs

Lines 108 to 110 in 71a2ac4

	// Match calls to `App::add_systems(schedule, systems)`
	if !crate::paths::APP.matches_ty(cx, receiver_ty)
	|| method_path.ident.name != sym::add_systems

But that only catches App::add_systems(...). These are all the systems I could find that can potentially add a system to FixedUpdate:

• App | SubApp
  • add_systems
  • configure_sets
  • get_schedule_mut -> Schedule
• Schedules
  • add_systems
  • configure_sets
  • entry -> Schedule
  • get_mut -> Schedule
• Schedule (that's guaranteed to be FixedUpdate, returned from another method)
  • add_systems
  • configure_sets
  • graph_mut (manually adding the system node to the graph, too complicated to check IMO)
• World
  • schedule_scope
  • try_schedule_scope

I don't think we need to check for all of these (some like Schedule::graph_mut() are particularly obtuse), but there is some low-hanging fruit like SubApp::add_systems()!