Merge branch 'jt/port-ci-whitespace-check-to-gitlab'

The "whitespace check" task that was enabled for GitHub Actions CI
has been ported to GitLab CI.

* jt/port-ci-whitespace-check-to-gitlab:
  gitlab-ci: add whitespace error check
  ci: make the whitespace report optional
  ci: separate whitespace check script
  github-ci: fix link to whitespace error
  ci: pre-collapse GitLab CI sections

ci/lib.sh

@@ -18,7 +18,7 @@ elif test true = "$GITLAB_CI"
 then
 	begin_group () {
 		need_to_end_group=t
-		printf "\e[0Ksection_start:$(date +%s):$(echo "$1" | tr ' ' _)\r\e[0K$1\n"
+		printf "\e[0Ksection_start:$(date +%s):$(echo "$1" | tr ' ' _)[collapsed=true]\r\e[0K$1\n"
 		trap "end_group '$1'" EXIT
 		set -x
 	}