Fix "TypeError: 'module' object is not callable" in test_commands.py' (#676).

Reviewed-on: https://projects.torsion.org/borgmatic-collective/borgmatic/pulls/676

tests/integration/borg/test_commands.py

@@ -1,6 +1,6 @@
 import copy
 
-import flexmock
+from flexmock import flexmock
 
 import borgmatic.borg.info
 import borgmatic.borg.list
@@ -105,4 +105,4 @@ def test_display_archives_info_command_does_not_duplicate_flags_or_raise():
 
         borgmatic.borg.info.display_archives_info(
             'repo', {}, '2.3.4', fuzz_argument(arguments, argument_name)
-        )
+        )