tests: replace imported module to avoid check-code.py error

This is a part of preparation to apply checking with check-code.py on
code fragments embedded in *.t test scripts.

tests/test-status.t

@@ -290,7 +290,7 b' hg status -A:'
 
   $ hg status -A -Tpickle > pickle
   >>> from __future__ import print_function
-  >>> import pickle
+  >>> from mercurial.util import pickle
   >>> data = sorted((x[b'status'].decode(), x[b'path'].decode()) for x in pickle.load(open("pickle", r"rb")))
   >>> for s, p in data: print("%s %s" % (s, p))
   ! deleted