gitlab: split alpha testing into a legacy container

gitlab: split alpha testing into a legacy container

The current bookworm compiler doesn't build the static binaries due to
bug #1054412 and it might be awhile before it gets fixed. The problem
of keeping older architecture compilers running isn't going to go away
so lets prepare the ground. Create a legacy container and move some
tests around so the others can get upgraded.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231029145033.592566-4-alex.bennee@linaro.org>