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

compiler/testData/diagnostics/tests/smartCasts/loops/assignWhenInsideWhileTrue.fir.kt

@@ -0,0 +1,17 @@
+// !CHECK_TYPE
+
+public fun foo(x: String?): Int {
+    var y: Any
+    loop@ while (true) {
+        y = when (x) {
+            null -> break@loop
+            "abc" -> return 0
+            "xyz" -> return 1
+            else -> x.length
+        }         
+        // y is always Int after when
+        checkSubtype<Int>(y)
+    }    
+    // x is null because of the break
+    return x.<!INAPPLICABLE_CANDIDATE!>length<!>
+}