### 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_enable == camera_3d_override) {
		return;
	}
	if (p_enable) {
		camera_3d_override.rid = RenderingServer::get_singleton()->camera_create();
	} else {
		RenderingServer::get_singleton()->free(camera_3d_override.rid);
		camera_3d_override.rid = RID();
	}
	if (p_enable) {
		RenderingServer::get_singleton()->viewport_attach_camera(viewport, camera_3d_override.rid);
	} else if (camera_3d) {
		RenderingServer::get_singleton()->viewport_attach_camera(viewport, camera_3d->get_camera());
	} else {
		RenderingServer::get_singleton()->viewport_attach_camera(viewport, RID());
	}
}
void Viewport::set_camera_3d_override_perspective(real_t p_fovy_degrees, real_t p_z_near, real_t p_z_far) {