checker: fix sumtype variant option type mismatch

[felipensp]

type Any = ?int | string
type Any2 = ?int | ?string

_ := ?Any(?string('baz')) // must be an error
_ := ?Any(string('baz')) // must be ok
_ := ?Any('baz') // must be ok

_ := ?Any2(?string('baz')) // must be ok
_ := ?Any2(string('baz')) // must be an error
_ := ?Any2('baz') // must be an error

[huly-for-github]

Connected to Huly®: V_0.6-22080

[spytheman]

Excellent work - less code, more features working 🥳 .