py/objtype: Validate super() arguments.

This fixes various null dereferencing and out-of-bounds access because
super_attr assumes the held obj is effectively an object of the held type,
which is now verified.

Fixes issue #12830.

Signed-off-by: stijn <stijn@ignitron.net>

tests/basics/builtin_super.py

@@ -0,0 +1,15 @@
+# Check that super rejects invalid arguments.
+try:
+    super(str, 0)
+except TypeError:
+    print("TypeError")
+
+try:
+    super(str, int)
+except TypeError:
+    print("TypeError")
+
+try:
+    super(0, int)
+except TypeError:
+    print("TypeError")