Improve Option::select() return type

[axlon]

This change adds a minor improvement to the return type of Option::select() for static analysis.

/** @var \PhpOption\Option<1|2|3> $option */
-PHPStan\dumpType($option->select(2)); // PhpOption\Option<1|2|3>
+PHPStan\dumpType($option->select(2)); // PhpOption\Option<2>