ResultTypeResolver: don't allow Nothing as ILT subtype

#KT-58379 Fixed

compiler/testData/diagnostics/tests/integerLiterals/sortedBy.fir.kt

@@ -1,25 +0,0 @@
-// WITH_STDLIB
-
-import Cause.*
-
-typealias ChallengeFunction = suspend (String) -> Unit
-
-enum class Cause {
-    FIRST,
-    SECOND,
-    ERROR,
-    LAST
-}
-
-class Some {
-    internal val register = mutableListOf<Pair<Cause, ChallengeFunction>>()
-
-    internal val challenges: List<ChallengeFunction>
-        get() = <!NEW_INFERENCE_ERROR!>register.filter { it.first != ERROR }.sortedBy {
-            when (it.first) {
-                FIRST -> 1
-                SECOND -> 2
-                else -> throw AssertionError()
-            }
-        }<!>.map { it.second }
-}

compiler/testData/diagnostics/tests/integerLiterals/sortedBy.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // WITH_STDLIB
 
 import Cause.*