tests: Fix import.

tests/basics/class_store_class.py

@@ -2,7 +2,7 @@
 # There was a bug in MicroPython that under some conditions class stored
 # in instance attribute later was returned "bound" as if it was a method,
 # which caused class constructor to receive extra argument.
-from collections import namedtuple
+from _collections import namedtuple
 
 _DefragResultBase = namedtuple('DefragResult', 'foo bar')