doc: fix list format in Developer's Certificate of Origin

This corresponds to the format at https://developercertificate.org/.

PR-URL: https://github.com/nodejs/node/pull/37138


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Pooja D P <Pooja.D.P@ibm.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>