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

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

@@ -0,0 +1,14 @@
+// !WITH_NEW_INFERENCE
+class Immutable(val x: String?) {
+    fun foo(): String {
+        if (x != null) return x
+        return ""
+    }
+}
+
+class Mutable(var y: String?) {
+    fun foo(): String {
+        if (y != null) return y
+        return ""
+    }
+}