Add non regression test for 4993

[VincentLanglet]

So the issue phpstan/phpstan#4993 is unclear to me

• It ask for no error on https://phpstan.org/r/5d0dc8ed-59c6-4b31-90a8-9c8bb85705fa but
  • There is already no error on PHP < 8
  • On PHP 8+ the error about NULL is legit since it's not a possible value. cf (Fix fgetcsv return type; never returns null since PHP8 #3712)

Also the issue talk about the fact the returned array is supposed to be non-empty ; which seems true and supported by psalm https://psalm.dev/r/3176073f08 so I updated the definition.

So I think that
Closes phpstan/phpstan#4993

[ondrejmirtes]

Thank you.