remote-mediawiki tests: use a 10 character password

remote-mediawiki tests: use a 10 character password

In more recent versions of MediaWiki this is a requirement, e.g. the
current stable version of 1.32.2.

The web installer now refuses our old 9 character password, the
command-line one (will be used in a subsequent change) will accept it,
but trying to use it in the web UI will emit an error asking the user
to reset the password. Let's use a password that'll just work and
allow us to log in as the admin user.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>