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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFir/invalidCode/duplicatedClassesFunctionParameter.kt

@@ -0,0 +1,6 @@
+class SomeClass {
+    val prop = "abc"
+}
+class SomeClass {
+    fun foo(<expr>p: Int</expr>) {}
+}