[13.x] Fix the ModelMakeCommand handle return type

[dfinchenko]

ModelMakeCommand::handle() is annotated @return void, but it returns false when the model already exists and the user declines to generate the additional components.

GeneratorCommand::handle(), which it overrides, is annotated @return bool|null, and ProviderMakeCommand already carries that same annotation on its own override.

PHPStan reports three errors on the file as it stands:

Return type (void) of method ModelMakeCommand::handle() should be compatible with
return type (bool|null) of method GeneratorCommand::handle()

Method ModelMakeCommand::handle() with return type void returns false but should not return anything.
Method ModelMakeCommand::handle() with return type void returns false but should not return anything.

Syncing the annotation with the parent's resolves all three, and makes the command analysable when it is extended in an application. Docblock only, no behavior change.