Fix import error for deepcopy (#2969)

Signed-off-by: kiersten-stokes <kierstenstokes@gmail.com>

lm_eval/tasks/squad_completion/task.py

 import re
+from copy import deepcopy
 from typing import List
 
 import numpy as np
-from deepcopy import deepcopy
 
 from lm_eval.api.instance import Instance
 from lm_eval.api.task import ConfigurableTask