www/gitlab-ce: bugfix update to 16.7.3

[Make chat_names table migration idempotent](gitlab-org/gitlab@1757965f503f2f0eb144731a982d4f83519e61d9) ([merge request](gitlab-org/gitlab!141704))

(cherry picked from commit 542d5518218e404dac0bc4d29f02e01453410db5)