[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/kt4332WhenBranches.fir.kt

@@ -0,0 +1,9 @@
+//KT-4332 when/smartcast underperforms
+
+fun testWhen(t: String?, x: String?): Int {
+    return when {
+        t == null -> 0
+        x == null -> t.length // Wrong error report here. t can be inferred as not-null. (And it actually does if you replace when with if/else if)
+        else -> (t + x).length
+    }
+}