[ci] remove unused imports in tests (#8707)

tests/python/test_ranking.py

@@ -1,8 +1,6 @@
 import itertools
 import os
 import shutil
-import urllib.request
-import zipfile
 
 import numpy as np
 from scipy.sparse import csr_matrix

tests/python/test_with_pandas.py

@@ -1,6 +1,3 @@
-import os
-import tempfile
-
 import numpy as np
 import pytest
 from test_dmatrix import set_base_margin_info