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

compiler/testData/diagnostics/tests/sealed/WithInterface.fir.kt

@@ -0,0 +1,10 @@
+interface Parent
+interface Child : Parent
+
+sealed class Page : Parent {
+  object One : Page(), Child
+  object Two : Page(), Child
+}
+
+// Ok: page is a Parent so it can be easily a Child
+fun test(page: Page): Boolean = page is Child