Add (failing) tests.

test/language/super/super_in_closure_in_inherited_method.wren

@@ -0,0 +1,11 @@
+class A {
+  callSuperToString {
+    return new Fn { super.toString }.call()
+  }
+
+  toString { "A.toString" }
+}
+
+class B is A {}
+
+IO.print((new B).callSuperToString) // expect: instance of B

test/language/super/super_in_inherited_method.wren

@@ -0,0 +1,9 @@
+class A {
+  callSuperToString { super.toString }
+
+  toString { "A.toString" }
+}
+
+class B is A {}
+
+IO.print((new B).callSuperToString) // expect: instance of B