Parsing of merge_request.created_at need to be done in SlackWebhook
The previous fix changed MergeRequest
but GitlabClient.merge_requests
doesn't return MergeRequest
objects, it returns Gitlab::ObjectifiedHash
objects where created_at is a string.
This fixes the issue by parsing the time once needed.
Fixes https://gitlab.com/gitlab-org/release-tools/issues/160
Edited by Rémy Coutable