Fix error border color for email input in feedback dialog (#3959)

This PR fixes the border color used when the email input in the feedback
dialog is invalid.

Previously this was hardcoded just to `red` instead of using the
appropriate color from the theme.

<img width="653" alt="Screenshot 2024-01-08 at 5 40 07 PM"
src="https://github.com/zed-industries/zed/assets/1486634/ea01cd76-d661-4512-b668-c82b8d00d84e">

Release Notes:

- Fixed the border color used for the email input in the feedback dialog
when an invalid email is entered.