### 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 (!p_node->is_visible()) {
		return nullptr; 
	}
	Transform2D matrix = p_xform * p_node->get_transform();
	
	if (matrix.basis_determinant() == 0.0f) {
		return nullptr;
	}
	Control *c = Object::cast_to<Control>(p_node);
	if (!c || !c->is_clipping_contents() || c->has_point(matrix.affine_inverse().xform(p_global))) {
		for (int i = p_node->get_child_count() - 1; i >= 0; i--) {
			CanvasItem *ci = Object::cast_to<CanvasItem>(p_node->get_child(i));
			if (!ci || ci->is_set_as_top_level()) {
				continue;
			}
			Control *ret = _gui_find_control_at_pos(ci, p_global, matrix);
			if (ret) {
				return ret;
			}
		}
	}
	if (!c || c->data.mouse_filter == Control::MOUSE_FILTER_IGNORE) {
		return nullptr;
	}
	matrix.affine_invert();
	if (!c->has_point(matrix.xform(p_global))) {
		return nullptr;
	}
	Control *drag_preview = _gui_get_drag_preview();