[Tests] Elaborate crashes in UnboundIrSerializationHandler

^KT-76998
diff --git a/native/native.tests/klib-ir-inliner/tests/org/jetbrains/kotlin/konan/test/inlining/AbstractNativeUnboundIrSerializationTest.kt b/native/native.tests/klib-ir-inliner/tests/org/jetbrains/kotlin/konan/test/inlining/AbstractNativeUnboundIrSerializationTest.kt
index a89561b..1387a13 100644
--- a/native/native.tests/klib-ir-inliner/tests/org/jetbrains/kotlin/konan/test/inlining/AbstractNativeUnboundIrSerializationTest.kt
+++ b/native/native.tests/klib-ir-inliner/tests/org/jetbrains/kotlin/konan/test/inlining/AbstractNativeUnboundIrSerializationTest.kt
@@ -167,7 +167,11 @@
             val lazyIrFunction = emulateInlineFunctionRepresentedByLazyIr(
                 functionUnderTest.fullyLinkedIrFunction, deserializedContainerSource
             )
-            functionUnderTest.partiallyLinkedIrFunction = deserializer.deserializeInlineFunction(lazyIrFunction) as IrSimpleFunction
+            val deserializeInlineFunction = deserializer.deserializeInlineFunction(lazyIrFunction)
+            require(deserializeInlineFunction != null) {
+                "Cannot deserialize inline fun: ${lazyIrFunction.dump()}"
+            }
+            functionUnderTest.partiallyLinkedIrFunction = deserializeInlineFunction as IrSimpleFunction
         }
 
         checkFunctionsSerialization(configuration, irBuiltIns, functionsUnderTest)