Tests on Maple were failing:
```
def test_retirement_for_multiple_users(self):
user_retirement_url = reverse('bulk_retirement_api')
expected_response = {
'successful_user_retirements': [self.user3.username, self.user4.username],
'failed_user_retirements': []
}
with self.settings(RETIREMENT_SERVICE_WORKER_USERNAME=self.user1.username):
response = self.client.post(user_retirement_url, {
"usernames": f'{self.user3.username},{self.user4.username}'
})
assert response.status_code == 200
> assert response.data == expected_response
E AssertionError: assert {'failed_user... 'testuser3']} == {'failed_user... 'testuser4']}
E Omitting 1 identical items, use -vv to show
E Differing items:
E {'successful_user_retirements': ['testuser4', 'testuser3']} != {'successful_user_retirements': ['testuser3', 'testuser4']}
E Use -v to get the full diff
```
`sorted(set(...))` still produces a list, and I guess we didn't care
about the order before, since it wasn't determined. So this should be
an acceptable change.
fee4ec26f5