Follow-up from "Docs: Restore ref attribute for Project Search API to search.md"

The following discussion from !21190 (merged) should be addressed:

• @rdickenson started a discussion: (+1 comment)

  @marcel.amirault - I looked at gitlab-foss@d46dca74 and indeed mention of the ref attribute was removed from the docs. Could you please look into this? I believe it should be reinstated, but I first wanted to check with you.