[FIR] NOTHING_TO_OVERRIDE diagnostic

compiler/testData/ir/irText/classes/kt45853.kt

@@ -1,4 +1,5 @@
 // TARGET_BACKEND: JVM
+// IGNORE_BACKEND_FIR: JVM_IR
 // SKIP_KT_DUMP
 // DUMP_EXTERNAL_CLASS: X
 // DUMP_EXTERNAL_CLASS: AX
@@ -8,6 +9,8 @@ abstract class A {
     abstract val a: A?
 }
 
+//Fir doesn't treat B.getA as an override, because it is not return-type compatible with AX.getA
+// Which might be correct behaivour. So disable fir till KT-46042
 class B() : AX() {
     override fun getA(): X? = super.a
 }