Mailchimp block: Handle embeds in Jetpack subscription emails

[arunsathiya]

Steps to reproduce

• Start with a site with Jetpack subscriptions enabled
• Subscribe to the site with your email
• Add a Mailchimp block to a post/page
• Publish

What is expected

The Mailchimp block shown on the email is handled better: either is ignored, a placeholder appears, or shows the actual block

What happens instead

The block appears broken, and shows all the success/failure messages at the same time

#manual-testing

[arunsathiya]

On an additional note, the above image is from ProtonMail. It does not seem to show the email input field, while it appears on Gmail.