[3.12] gh-127522: wsgiref: indicate that `start_response` objects should follow a specific protocol (GH-127525) (GH-130505)

(cherry picked from commit 39ba4b6619026bbe65c5844702a8a0bb6e75c4f7)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>