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

compiler/testData/diagnostics/tests/backingField/FieldShadow.fir.kt

@@ -0,0 +1,8 @@
+class My {
+    // No initialization needed because no backing field
+    val two: Int
+        get() {
+            val field = 2
+            return field
+        }
+}