[ticket/11538] Add admin as admins leader and moderator in memberlist_test

Removing the admin user from the admin and moderator group in memberlist_test
potentially breaks other tests, i.e. the ucp groups test.

PHPBB3-11538
Merge remote-tracking branch 'marc1706/ticket/11538' into develop

* marc1706/ticket/11538:
  [ticket/11538] Add admin as admins leader and moderator in memberlist_test
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11587
[ticket/11587] Add functional tests for group teampage settings

The group_legend and group_teampage settings, which are needed for the
teampage, are tested with these newly added functional tests.
Duplicate code has been reduced as much as possible.

PHPBB3-11587