gitlab-ci: move `tidy` back to the `build` stage
It takes about 10 minutes now with clang-tidy-cache
doing its thing.
GitLab update will be applied on June 28th, between 8am and 10:30am, EDT (UTC-04:00). This site may have intermittent delays during that time.
It takes about 10 minutes now with clang-tidy-cache
doing its thing.