The current setup causes the Security team and the other owners of
.github/workflows to **not** be pinged for the
check-format/codeowners-v2/nixpkgs-vet workflows. This was highly likely
unintended when adding those additional rules, so removing them.

Also, we have some owners looking after `workflows/`, but not `ci/` -
and some the other way around. This doesn't make much sense to me, since
both parts depend on each other very much.

(cherry picked from commit b98e7bb)