Editorial: fix a markup typo

[zcorpan]

The following tasks have been completed:

• [x] Confirmed there are no ReSpec errors/warnings.
• [ ] Modified Web platform tests N/A
• [ ] Modified MDN Docs N/A
• [ ] Has undergone security/privacy review N/A

Implementation commitment: N/A

Optional, impact on Payment Handler spec? None. I checked if it had the same typo, and it did not.

---

Preview | Diff

[w3cbot]

zcorpan marked as non substantive for IPR from ash-nazg.

[marcoscaceres]

(Blocked on updating auto-pub script… will merge soon)