Fix another import error.

In 2018, all imports came from the test.support package. They are now
splitted among various subpackages.

Author: s-ball

Lib/test/test_tools/test_i18n.py

@@ -9,7 +9,8 @@
 
 from test.support.script_helper import assert_python_ok, assert_python_failure
 from test.test_tools import skip_if_missing, toolsdir
-from test.support.os_helper import temp_cwd, temp_dir, unload, change_cwd
+from test.support.os_helper import temp_cwd, temp_dir, change_cwd
+from test.support.import_helper import unload
 
 
 skip_if_missing()