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

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

@@ -0,0 +1,22 @@
+// !CHECK_TYPE
+
+fun bar(): Boolean { return true }
+
+public fun foo(x: String?): Int {
+    var y: Int?
+    y = 0
+    loop@ do {
+        y += when (x) {
+            null -> break@loop
+            "abc" -> return 0
+            "xyz" -> return 1
+            else -> x.length
+        }         
+        // y is always Int after when
+        checkSubtype<Int>(y)
+    } while (bar())
+    // y is always Int even here
+    checkSubtype<Int>(y)
+    // x is null because of the break
+    return x.<!INAPPLICABLE_CANDIDATE!>length<!>
+}