Migration: header->expect & impl->actual in IDEA test data

idea/testData/multiModuleQuickFix/memberValToExtensionByHeader/header/header.kt

@@ -1,5 +1,5 @@
 // "Convert member to extension" "true"
 
-header class Foo {
+expect class Foo {
     val <caret>foo: Int
 }

idea/testData/multiModuleQuickFix/memberValToExtensionByHeader/header/header.kt.after

@@ -1,6 +1,6 @@
 // "Convert member to extension" "true"
 
-header class Foo {
+expect class Foo {
 }
 
 expect val Foo.foo: Int