Add test for obsolete issue

#KT-38161 Obsolete

compiler/testData/diagnostics/tests/funInterface/funInterfaceConversionOnReceiver.fir.kt

@@ -0,0 +1,9 @@
+fun interface Bar {
+    fun invoke(): String
+}
+
+operator fun Bar.plus(b: Bar): String = invoke() + b.invoke()
+
+fun box(): String {
+    return { "O" } <!INAPPLICABLE_CANDIDATE!>+<!> { "K" }
+}