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

compiler/testData/diagnostics/tests/dataFlow/assignment/kt6118.fir.kt

@@ -0,0 +1,16 @@
+// KT-6118 Redundant type cast can be not redundant?
+
+fun foo(o: Any) {
+    if (o is String) {
+        val s = o as String
+        s.length
+    }
+}
+
+fun foo1(o: Any) {
+    if (o is String) {
+        o.length
+        val s = o
+        s.length
+    }
+}