OSEC-2026-30 Ephemeron data is freed while still referenced when the key is an `Infix_tag` closure

Summary In OCaml before 4.14.5, when the key of an ephemeron is a closure with Infixtag a function of a mutually recursive group that is not the first function, the mark phase does not keep the ephemeron's data alive, although the key is alive. The clean phase does treat the key as alive, so it...