Email validation error in view needs improvement (there's no feedback when the input is selected, needs a message)

Error state:

Unfocused	Focused

I suspect this has accessibility issues, at the very least an error message should be attached.

via Automattic/wp-calypso#30275 (comment)

To reproduce

1. Add a Subscription block instructions
2. Publish
3. View the block
4. Enter invalid email
5. 😕

cc: @jeffersonrabb @artpi