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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFir/wholeDeclaration/nestedClassScript.kts

@@ -0,0 +1,7 @@
+class Y {
+    <expr>
+    class X {
+        fun y(): String
+    }
+    </expr>
+}