KMP: Put "prohibit member scope mismatch for non-final expect" under the flag

^KT-61668 Fixed

Review: https://jetbrains.team/p/kt/reviews/12062/timeline

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -278,6 +278,10 @@ enum class LanguageFeature(
     ProhibitUsingNullableTypeParameterAgainstNotNullAnnotated(sinceVersion = KOTLIN_1_9), // KT-36770
     NoSourceCodeInNotNullAssertionExceptions(KOTLIN_1_9, sinceApiVersion = ApiVersion.KOTLIN_1_4, kind = OTHER), // KT-57570
 
+    // 1.9.20 KMP stabilization. Unfortunately, we don't have 1.9.20 LV. So LV=1.9 is the best we can do.
+    // At least there won't be false positives for 1.8 users
+    MultiplatformRestrictions(KOTLIN_1_9, kind = BUG_FIX), // KT-61668
+
     // End of 1.* language features --------------------------------------------------
 
     // 2.0