fix spaceship operator for large constant unions

[schlndh]

This PR fixes a false positive encountered by #2885 . I simplified it to smaller example: https://phpstan.org/r/892eed14-49b8-4a98-b591-90cf5741a99e

This scenario only happens with bleeding edge enabled. Without it the constant union doesn't make it into getSpaceshipType due to

phpstan-src/src/Type/Generic/TemplateTypeTrait.php

Line 269 in 4e1bfac

if (!BleedingEdgeToggle::isBleedingEdge() && $this->shouldGeneralizeInferredType()) {

As far as I can tell, the spaceship operator should always return -1, 0, or 1: https://3v4l.org/FVeq7

[ondrejmirtes]

Thank you!