[IR] IrExpectActualAnnotationMatchingChecker: add elaboration comment

Review: https://jetbrains.team/p/kt/reviews/13094/timeline

compiler/ir/ir.actualization/src/main/kotlin/org/jetbrains/kotlin/backend/common/actualizer/checker/IrExpectActualAnnotationMatchingChecker.kt

@@ -25,6 +25,8 @@ internal object IrExpectActualAnnotationMatchingChecker : IrExpectActualChecker
             if (expectSymbol is IrTypeParameterSymbol) {
                 continue
             }
+            // If the expect declaration is fake-override and is incompatible, then it means that it was overridden on actual.
+            // In such case, regular rules for annotations on overridden declarations apply.
             if (expectSymbol.isFakeOverride) {
                 continue
             }