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

compiler/testData/diagnostics/tests/smartCasts/ifWhenExprNonNull.fir.kt

@@ -0,0 +1,13 @@
+fun baz(s: String?): String {
+    val t = if (s == null) {
+        ""
+    }
+    else {
+        val u: String? = null
+        when (u) {
+            null -> ""
+            else -> u
+        }
+    }
+    return t
+}