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

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

@@ -0,0 +1,6 @@
+fun bar(x: Int?): Int {
+    if (x != null) return -1
+    if (x == null) return -2
+    // Should be unreachable
+    return 2 + 2
+}