fix: use func_num_args() to determine if $return should be used for Database\Model (#30)

It was not possible to set the return type explicitly as `null`, since that was the value we checked for if we should return the value of `$return` or not. We're not checking the total amount of arguments provided to check if a `$return` value was passed or not.

Reviewed-on: https://codeberg.org/vlw/scaffold/pulls/30

src/Database/Model.php

@@ -109,6 +109,6 @@
 				->where($this->where)
 				->update([$key => $value]);
 
-			return $return ?? $value;
+			return func_num_args() === 2 ? $value : $return;
 		}
 	}