[10.x] Fix Factory::configure() return type

[axlon]

TL;DR: Small doc block fix

The Factory::configure() method currently indicates that it returns $this (the exact instance the method was called on), but this is not always true. For example, when calling the afterCreating() method a new factory instance is created, e.g.:

    /**
     * @return static
     */
    public function configure(): static
    {
        return $this->afterCreating(static function (MyModel $model) {
            doSomethingWithTheModel($model);
        });
    }

For most IDEs this isn't an issue because they will handle $this and static the same way, but tools like PHPStan do differentiate between them. When using PHPStan strict rules, you would get an error here because the @return static in the example doesn't comply with the @return $this on the base factory, and if you changed it to @return $this it will also fail because you are in fact returning a new instance (the return type for afterCreating() is documented as static).

This PR solves this by fixing the return type on the configure method, this is not a breaking change as its only a docblock type and static encompasses $this so anyone using @return $this is still fine.