tests/basics: Change dict_fromkeys test so it doesn't use generators.

And then it can run with the native emitter.

tests/basics/dict_fromkeys.py

@@ -8,6 +8,6 @@ l = list(d.values())
 l.sort()
 print(l)
 
-# argument to fromkeys is a generator
-d = dict.fromkeys(i + 1 for i in range(1))
+# argument to fromkeys has no __len__
+d = dict.fromkeys(reversed(range(1)))
 print(d)