[NI] Fix determination of completion mode. #KT-30406 Fixed

compiler/testData/diagnostics/tests/controlStructures/kt30406.kt

@@ -0,0 +1,16 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_EXPRESSION
+// !CHECK_TYPE
+// Issue: KT-30406
+
+interface Option<out T> {
+    val s: String
+}
+class Some<T>(override val s: String) : Option<T>
+class None(override val s: String = "None") : Option<Int>
+
+fun test(a: Int): Option<Any> =
+    <!DEBUG_INFO_EXPRESSION_TYPE("Option<kotlin.Any>")!>if (a == 239)
+        <!DEBUG_INFO_EXPRESSION_TYPE("Some<kotlin.Any>")!>Some("239")<!>
+    else
+        <!DEBUG_INFO_EXPRESSION_TYPE("None")!>None()<!><!>