pickle: test_pickle.py: Update for bytes being returned/consumed.

pickle/test_pickle.py

@@ -5,6 +5,7 @@ import io
 
 def roundtrip(val):
     t = pickle.dumps(val)
+    assert isinstance(t, bytes)
     t = pickle.loads(t)
     assert t == val
 
@@ -18,7 +19,7 @@ roundtrip([1, 2])
 roundtrip({1:2, 3: 4})
 
 try:
-    pickle.loads("1; import micropython")
+    pickle.loads(b"1; import micropython")
     assert 0, "SyntaxError expected"
 except SyntaxError:
     pass