Bug 30595: Prevent update_child_to_adult.t to fail randomly

Bug 30595: Prevent update_child_to_adult.t to fail randomly

t/db_dependent/selenium/update_child_to_adult.t ..         # Looks like you planned 3 tests but ran 2.

    #   Failed test 'Update child to adult'
    #   at t/db_dependent/selenium/update_child_to_adult.t line 132.
    # Looks like you planned 3 tests but ran 2.
    # Looks like you failed 1 test of 2 run.
t/db_dependent/selenium/update_child_to_adult.t .. 1/1
 #   Failed test 'Update child to patron'
 #   at t/db_dependent/selenium/update_child_to_adult.t line 153.
Cannot wait more for element '//input[@type="submit"]' to be visible at /kohadevbox/koha/t/lib/Selenium.pm line 189.

It happens when there are too many patron's categories and the submit
button is not in the viewport.

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>