git-remote-entire: regression test for helper-status on send-pack error

handlePush relays send-pack's helper-status lines to stdout before checking the subprocess exit code, so per-ref rejections (branch protection, D/F conflict, server hook decline) reach git's transport-helper.c and render as ! [remote rejected] <ref> (<reason>). Pin that ordering: a PATH-injected shell stub plays the role of git send-pack, emits an empty wrapped request followed by a trailing flush + error <ref> ... helper-status line, and exits 1. The test asserts that handlePush both returns the exit error AND has already written the helper-status to stdout. Verified failing against the pre-fix push.go (helperStatus empty in stdout).