CI Slack integration: build status message broken

The link to the build is broken in Slack build status messages. Probably because the posted url is a relative url and not an absolute one. For quick reference, the message is build here. A screenshot of the broken message:

mentioned in issue #2572 (closed)

Did it work in 7.14?

Unfortunately, I do not know the last working version number (we use the hosted gitlab/gitlab-ci versions). However I verified it was still working yesterday. The last working link was an absolute url: https://ci.gitlab.com/projects/....

This is regression

!1391 (merged)

Added ~19173 label

I think this was intended to be closed by !1391 (merged).

Status changed to closed