Fix str_contains() never returns 0 on OnlyRuleResolver

[samsonasik]

PHPStan somehow detect str_contains() as union

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PHPStan\Type\UnionType #22767
   types: array (2)
   |  0 => PHPStan\Type\IntegerRangeType #20331
   |  |  min: 0
   |  |  max: null
   |  1 => PHPStan\Type\Constant\ConstantBooleanType #22757
   |  |  value: false
   normalized: true
   sortedTypes: true
   cachedDescriptions: array (1)
   |  4 => 'int<0, max>|false'

Ref #6545 (review)