CI: test_admin_edits_hotp_secret is flaky

[eloquence]

Example flake: https://circleci.com/gh/freedomofpress/securedrop/30247

Relevant output:

_______________ TestAdminInterface.test_admin_edits_hotp_secret ________________

self = <tests.functional.test_admin_interface.TestAdminInterface object at 0x7fde8027d390>

    def test_admin_edits_hotp_secret(self):
        self._admin_logs_in()
        self._admin_visits_admin_interface()
        self._admin_adds_a_user()
        self._admin_visits_edit_user()
>       self._admin_visits_reset_2fa_hotp()

/home/circleci/project/securedrop/tests/functional/test_admin_interface.py:21: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/home/circleci/project/securedrop/tests/functional/journalist_navigation_steps.py:750: in _admin_visits_reset_2fa_hotp
    self.wait_for(lambda: self.driver.find_elements_by_css_selector(
/home/circleci/project/securedrop/tests/functional/functional_test.py:291: in wait_for
    return function_with_assertion()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

    self.wait_for(lambda: self.driver.find_elements_by_css_selector(
>       "#button-reset-two-factor-hotp")[0])
E   IndexError: list index out of range

/home/circleci/project/securedrop/tests/functional/journalist_navigation_steps.py:751: IndexError

[redshiftzero]

Assigning myself because I think the diff in fix-flake-4541 will also resolve this - I hit this when running test_admin_edits_hotp_secret in a loop and I added logic handling the IndexError