tests/basics: Add test for super() when self is closed over.

tests/basics/class_super_closure.py

+# test that no-arg super() works when self is closed over
+
+class A:
+    def __init__(self):
+        self.val = 4
+    def foo(self):
+        # we access a member of self to check that self is correct
+        return list(range(self.val))
+class B(A):
+    def foo(self):
+        # self is closed over because it's referenced in the list comprehension
+        # and then super() must detect this and load from the closure cell
+        return [self.bar(i) for i in super().foo()]
+    def bar(self, x):
+        return 2 * x
+
+print(A().foo())
+print(B().foo())