cli/task: Ensure cli output is always in the same order

This test is flaky [1]

• [1] https://jenkins.softwareheritage.org/job/DSCH/job/tests-on-diff/380/testReport/junit/.tox.py3.lib.python3.7.site-packages.swh.scheduler.tests/test_cli/test_list_tasks_type/

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Migrated from D5916 (view on Phabricator)