Also setup default settings values for 'settings.gradle.kts'.

^KT-45745 In Progress

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/testDsl.kt

@@ -281,7 +281,8 @@ private fun Path.addDefaultBuildFiles() {
 }
 
 private fun TestProject.agreeToBuildScanService() {
-    settingsGradle.append(
+    val settingsFile = if (Files.exists(settingsGradle)) settingsGradle else settingsGradleKts
+    settingsFile.append(
         """
             
         gradleEnterprise {