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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFir/expressions/whenExpressionScript.kts

@@ -0,0 +1,6 @@
+fun foo(x: Any): String {
+    return <expr>when (x) {
+        is String -> "1"
+        else -> "2"
+    }</expr>
+}