Finalisation error on using add_task

```sh
Name: pytest-sanic
Version: 1.9.1
---
Name: sanic
Version: 22.12.0
```

Got following error on running tests on routes that use `add_task`. 

```
sanic_routing.exceptions.FinalizationError: Cannot finalize router more than once.
```

Was working fine with older Sanic version.