Kotlin: exclude Kotlin files from java/underscore-identifier

java/ql/src/Compatibility/JDK9/UnderscoreIdentifier.ql

@@ -22,7 +22,7 @@ class IdentifierElement extends Element {
 
 from IdentifierElement e, string msg
 where
-  e.fromSource() and
+  e.getCompilationUnit().isJavaSourceFile() and
   not e.(Constructor).isDefaultConstructor() and
   (
     e.getName() = "_" and

java/ql/test/kotlin/query-tests/UnderscoreIdentifier/UnderscoreIdentifier.expected

@@ -1 +0,0 @@
-| Test.kt:8:14:8:25 | Exception _ | Use of underscore as a one-character identifier. |