[MozFest] Call to action block on MozFest doesn't allow for mailto links

[marcwalsh]

Describe the bug

I'm creating a Sponsors page on the MozFest website where the CTA is to email the team.
When adding the 'Call to action' block and adding a mail to link (eg: mailto:sponsor@mozillafestival.org) I get a validation error saying that I need to 'enter a valid URL'

To Reproduce

Steps to reproduce the behavior:

1. Use the Call to action block on the MozFest website
2. Add a mail to link in the Link URL field
3. Press Save/Publish
4. See validation error

Expected behavior

I'm able to add a mailto link as a valid URL

Additional context

This is the page I'm trying to add this to: https://www.mozillafestival.org/cms/pages/27424/edit/

Other blocks like buttons allow me to add mailto link

┆Issue is synchronized with this Jira Story

[mmmavis]

I think updating the regex here should solve the issue. I will bring this ticket to our next ticket triage session.