Better message if override violates Liskov substitution principle

Some users don't understand why mypy complains about incompatible overrides. We could add an extra note in cases where the argument type is narrower in an override or the return type is wider (or all incompatible overrides). The note could mention Liskov substitution principle and add a link to mypy documentation (add a new section to https://mypy.readthedocs.io/en/latest/common_issues.html perhaps). We can also mention that # type: ignore[override] can be used to silence this error.

#7992 is an example where this came up, but several users have been confused about this.

Empieza por localizar el tratamiento del diagnóstico incompatible-override de mypy y revisar la documentación sobre problemas comunes enlazada en el issue. Consulta el issue #7992 para ver el ejemplo que motiva el cambio. Se considerará terminado cuando los casos relevantes de override expliquen el principio de sustitución de Liskov, enlacen a la documentación y mencionen la opción type-ignore para override, con tests que cubran el mensaje.