updateTemplate patches fields on an existing template.
Example
Inputs
templateId: number | string is required. Optional fields are templateName,
subject, registered sender, htmlContent (minimum 11 characters), public
htmlUrl, attachmentUrl, isActive, replyTo, tag, and toField.
account selects the Brevo binding.
Output
ReturnsSignal<void> after Brevo accepts the update. The action does not
retrieve the resulting template; use getTemplate when you need confirmation
of provider-normalized content. Avoid supplying both HTML sources in one patch.