### Godot version

v4.0.beta.custom_build [0a9e6e478]

### System information

Ubuntu, Nvidia, Vulkan

### Issue description

When a Camera2D is freed - either explicitly or by being a child of a scene that is being switched away from via a method like `get_tree().change_scene_to_file()` - then this camera somehow stays active instead of Godot properly switching to no-camera-mode.

`get_viewport().get_camera_2d()` then returns all sorts of funny things from `<Freed Object>`  (it's supposed to return `null`) to arbitrary nodes of the current scene (not cameras).

This can lead to crashes.

### Steps to reproduce

checkout the MRP.

note that the "Go to scene 2" button switches places after pressing it.
that is because a camera is still active that does not exist in the current tree.

restart it a couple of times and spam the "Go to scene 2" button.
notice the garbage output.

### Minimal reproduction project

[godot_4_camera_bug.zip](https://github.com/godotengine/godot/files/10560455/godot_4_camera_bug.zip)
}
		if (over != gui.mouse_over) {
			_drop_mouse_over();
			_gui_cancel_tooltip();
			if (over) {
				if (!gui.mouse_over) {
					_drop_physics_mouseover();
				}
				_gui_call_notification(over, Control::NOTIFICATION_MOUSE_ENTER);
				gui.mouse_over = over;
			}
		}
		if (gui.mouse_focus) {
			over = gui.mouse_focus;
		}
		DisplayServer::CursorShape ds_cursor_shape = (DisplayServer::CursorShape)Input::get_singleton()->get_default_cursor_shape();
		if (over) {
			Transform2D localizer = over->get_global_transform_with_canvas().affine_inverse();
			Size2 pos = localizer.xform(mpos);
			Vector2 velocity = localizer.basis_xform(mm->get_velocity());
			Vector2 rel = localizer.basis_xform(mm->get_relative());
			mm = mm->xformed_by(Transform2D()); 
			mm->set_global_position(mpos);
			mm->set_velocity(velocity);
			mm->set_relative(rel);
			if (mm->get_button_mask().is_empty()) {
				
				bool is_tooltip_shown = false;
				if (gui.tooltip_popup) {
					if (gui.tooltip_control) {