This fixes the build with gcc 14:
contrib/kyua/engine/prepare/prepare_all.cpp:56:16: error: declaration of 'handler' shadows a member of 'engine::prepare::prepare_all' [-Werror=shadow]
56 | for (auto& handler : prepare::handlers()) {
| ^~~~~~~In file included from /home/siva/f/main/contrib/kyua/engine/prepare/prepare_all.hpp:35,
from /home/siva/f/main/contrib/kyua/engine/prepare/prepare_all.cpp:29:
/home/siva/f/main/contrib/kyua/engine/prepare/prepare.hpp:51:15: note: shadowed declaration is here
51 | class handler {
| ^