ci: Upgrade clang-16 job to clang-18
Upgrade the clang-16 job in the CI by a clang-18 job. Clang-18 is the latest stable release of clang compiler, so it makes sense to start testing it.
Upgrade the clang-16 job in the CI by a clang-18 job. Clang-18 is the latest stable release of clang compiler, so it makes sense to start testing it.