### Godot version

v4.0 rc6

### System information

Windows 10

### Issue description

When using a ViewportTexture from a SubViewport on a TextureRect, it throws errors after running the scene once and then switching scenes in the editor.
![Pasted image 20230227212626](https://user-images.githubusercontent.com/44676282/221680047-984fa03e-33d1-4856-9a7f-1700b28423cf.png)


### Steps to reproduce

Run the canvas-scene once.
Switch to another scene in the editor.
Switch back to the canvas-scene

### Minimal reproduction project

[ViewportTextureError.zip](https://github.com/godotengine/godot/files/10844099/ViewportTextureError.zip)

ERR_MAIN_THREAD_GUARD;
	if (p_disable == disable_input) {
		return;
	}
	if (p_disable) {
		_drop_mouse_focus();
		_mouse_leave_viewport();
		_gui_cancel_tooltip();
	}
	disable_input = p_disable;
}
bool Viewport::is_input_disabled() const {
	ERR_READ_THREAD_GUARD_V(false);
	return disable_input;
}
Variant Viewport::gui_get_drag_data() const {
	ERR_READ_THREAD_GUARD_V(Variant());
	return gui.drag_data;
}
PackedStringArray Viewport::get_configuration_warnings() const {
	ERR_MAIN_THREAD_GUARD_V(PackedStringArray());
	PackedStringArray warnings = Node::get_configuration_warnings();
	if (size.x <= 1 || size.y <= 1) {
		warnings.push_back(RTR("The Viewport size must be greater than or equal to 2 pixels on both dimensions to render anything."));
	}
	return warnings;
}
void Viewport::gui_reset_canvas_sort_index() {