Step 5d added ~150 lines to http_server.erl bringing it to ~1180
lines. erlang-load-module on this port scales superlinearly with
function count, so three more http_*.sh tests' internal sx_server
timeout (M1 default 240s) was no longer enough.
Bumped to 600s — matches the headroom the other eight http_*.sh
tests got in the Step 5d commit. Background-gate verification
flagged these three (no behaviour change; just budget).
http_publish 10/10, http_post_format 13/13, http_multi_actor 41/41
all green at 600s.
