tests/extmod: Split json.loads of bytes/bytearray into separate test.

Because this functionality was introduced in Python 3.6.

tests/extmod/ujson_loads.py

@@ -37,10 +37,6 @@ my_print(json.loads('"abc\\uabcd"'))
 # whitespace handling
 my_print(json.loads('{\n\t"a":[]\r\n, "b":[1], "c":{"3":4}     \n\r\t\r\r\r\n}'))
 
-# loading from bytes and bytearray
-my_print(json.loads(b'[1,2]'))
-my_print(json.loads(bytearray(b'[null]')))
-
 # loading nothing should raise exception
 try:
     json.loads('')

tests/extmod/ujson_loads_bytes.py

+# test loading from bytes and bytearray (introduced in Python 3.6)
+
+try:
+    import ujson as json
+except ImportError:
+    try:
+        import json
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+print(json.loads(b'[1,2]'))
+print(json.loads(bytearray(b'[null]')))

tests/extmod/ujson_loads_bytes.py.exp

+[1, 2]
+[None]