Update docs.gitlab-ci.yml to use trigger-build script
What does this MR do?
Matches the updates made in omnibus-gitlab!4443 (merged) due to gitlab!37082 (merged) (raised as a result of this conversation).
Why was this MR needed?
Failing docs review app builds in the Runner project as reported by @sselhorn here !2296 (merged) led me to realize the same change was needed there.
$ wget https://gitlab.com/gitlab-org/gitlab-ce/raw/master/scripts/trigger-build-docs
Connecting to gitlab.com (172.65.251.78:443)
Connecting to gitlab.com (172.65.251.78:443)
wget: server returned error: HTTP/1.1 404 Not Found
ERROR: Job failed: exit code 1
What's the best way to test this MR?
Merge and then attempt to deploy a docs review app via a new pipeline on !2296 (merged)