Fix would-be regression

https://gitlab.com/gitlab-org/gitlab-ce/commit/57e3e942de1adef2c8621905370f07d7da7870c4

I changed it to a separate condition rather than depending on the order of the case-when statements to prevent this mistake again.

lib/gitlab/git_access.rb

@@ -243,9 +243,7 @@ module Gitlab
         when User
           actor
         when Key
-          actor.user
-        when DeployKey
-          nil
+          actor.user unless actor.is_a?(DeployKey)
         when :ci
           nil
         end