[CI] Update email/URL instructions in `registry-entry.yml` to avoid workflow check errors

[vitorvasc]

Description

The registry-entry.yml template doesn't clearly state that when adding a registry entry, the author must provide either an email or a URL under authors. As both fields are currently flagged as "optional", contributors who follow the template as written may omit both, which causes the registry validation workflow to fail.

Example error form the workflow logs:

[09:06:29] Starting 'validate-registry'...
Error: An author must have an email or a URL
Error: must match "else" schema
[09:06:30] 'validate-registry' errored after 392 ms

---

This requirement isn't clear as it could be in the current registry-entry.yml template, so I'll treat this as an action item to improve that documentation.

Originally posted by @vitorvasc in #8563 (comment)

[pmady]

As i am first time contributor for this repo, can i pick this?

[vitorvasc]

Hi @pmady! Yes, please feel free to submit a PR. You might also want to take a look at #5511, they're both linked. :)

[pmady]

@vitorvasc Here is the PR #8592. Thanks