Fix test: check highlighting only in one direction

Otherwise, when we check the highlighting on one of the files, the text
of the other still contains the <lineMarker> annotation and can't be
indexed as valid Kotlin code.

idea/testData/multiModuleLineMarker/fromClassToAlias/jvm/jvm.kt

@@ -1,2 +1,4 @@
-impl typealias <lineMarker>Header</lineMarker> = String
+// !CHECK_HIGHLIGHTING
+
+impl typealias Header = String