Fix compiler tests

compiler/testData/diagnostics/tests/incompleteCode/plusOnTheRight.kt

@@ -2,7 +2,7 @@
 package a
 
 class MyClass1 {
-    public fun plus() {}
+    public operator fun plus() {}
 }
 
 fun main(arg: MyClass1) {

compiler/testData/diagnostics/tests/incompleteCode/plusOnTheRight.txt

@@ -7,7 +7,7 @@ package a {
         public constructor MyClass1()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-        public final fun plus(): kotlin.Unit
+        public final operator fun plus(): kotlin.Unit
         public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
     }
 }