[LL FIR] rename testdata to testData to avoid copyright generation

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/fileStructure/localClassScript.kts

@@ -0,0 +1,9 @@
+/* RootScriptStructureElement */fun a() {/* DeclarationStructureElement */
+    class X
+}
+
+class Y {/* ClassDeclarationStructureElement */
+    fun b() {/* DeclarationStructureElement */
+        class Z
+    }
+}