Consider using one `postgres` instance for testing

[kondratevdev]

https://github.com/Peopl3s/clean-architecture-fastapi-project-template/blob/da3e0072b72e7ca2461e5edfe03ebe519dd63b54/{{cookiecutter.project_slug}}/docker-compose.yml#L26

I think there is no need to use a separate postgres instance for testing. This can be done by creating a new database inside the current postgres instance.