tests/docker: update debian i686 and mipsel images to bookworm

tests/docker: update debian i686 and mipsel images to bookworm

Whatever issues there were which stopped these being updates when the
rest were have now been resolved. However mips64el continues to be
broken so don't update it here.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240910173900.4154726-3-alex.bennee@linaro.org>
(cherry picked from commit 19d2111059c87d3f58349f27b9be9dee81fc1681)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>