Thanks @liyishuai coq-http is now back in Coq CI: coq/coq#19679
However, next time you plan such a change in the build process of something in Coq CI, please advise Coq devs in advance so as to find a way to minimize diisruption there (with the previous parsec issue, coq-http has been down for more than a week in Coq CI) and, maybe more importantly, Coq dev work to adapt to your changes. Unfortunately, updating opam packages is not enough since Coq CI has its own configuration, not based on opam.
FWIW, I'm also updating the Nix packages: NixOS/nixpkgs#348516

Maybe worth integrating a GitHub action that monitors the OPAM file updates and sends notifications to Coq devs.

Well, most developers don't even think about updating the opam files, you were rather the good student on that front. In any case, this would be too late. No, that kind of things just need to be planned and discussed in advance.