[K/N][test] Get rid of the Gradle warning in the old infra

This outputDirectory property was marked incorrectly as OutputDirectory.
It points to test build tasks output and should not be considered during
up-to-date checks.

Merge-request: KT-MR-9019
Merged-by: Pavel Punegov <Pavel.Punegov@jetbrains.com>

kotlin-native/build-tools/src/main/kotlin/org/jetbrains/kotlin/KotlinNativeTest.kt

@@ -41,7 +41,7 @@ abstract class KonanTest : DefaultTask(), KonanTestExecutable {
     /**
      * Test output directory. Used to store processed sources and binary artifacts.
      */
-    @get:OutputDirectory
+    @get:Internal
     abstract val outputDirectory: String
 
     /**