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

compiler/testData/diagnostics/tests/smartCasts/varnotnull/inference.fir.kt

@@ -0,0 +1,21 @@
+// See KT-969
+fun f() {
+  var s: String?
+  s = "a"
+  var s1 = "" // String � ?
+  if (s != null) {    // Redundant
+    s1.length
+    // We can do smartcast here and below
+    s1 = s.toString() // return String?
+    s1.length
+    s1 = s
+    s1.length
+    // It's just an assignment without smartcast
+    val s2 = s
+    // But smartcast can be done here
+    s2.length
+    // And also here
+    val s3 = s.toString()
+    s3.length
+  }
+}