docker: Fix HOME setting (fixes #6234) (#6235)

su-exec sets $HOME, and we used to have this env call in there to fix
that up. It disappeared in the latest entrypoint.sh rewrite.

script/docker-entrypoint.sh

@@ -4,4 +4,4 @@ set -eu
 
 chown "${PUID}:${PGID}" "${HOME}" \
   && exec su-exec "${PUID}:${PGID}" \
-     "$@"
+     env HOME="$HOME" "$@"