Check class source in bytecode listing tests

compiler/testData/codegen/bytecodeListing/privateNestedClassInInterface.txt

@@ -1,10 +1,12 @@
 @kotlin.Metadata
 final class IFoo$Nested {
+    // source: 'privateNestedClassInInterface.kt'
     public method <init>(): void
     private final inner class IFoo$Nested
 }
 
 @kotlin.Metadata
 public interface IFoo {
+    // source: 'privateNestedClassInInterface.kt'
     private final inner class IFoo$Nested
 }