compiler testdata: s/trait/interface

compiler/testData/diagnostics/tests/multimodule/duplicateMethod/extensionMatch.kt

@@ -4,7 +4,7 @@
 // FILE: a.kt
 package p
 
-public trait B {
+public interface B {
     public fun String.getParent(): B?
 }
 
@@ -21,7 +21,7 @@ public class C : B {
 // FILE: b.kt
 package p
 
-public trait B {
+public interface B {
     public fun String.getParent(): B?
 }