Incomplete form fields highlighted only by color + toolip

WCAG 1.4.1 Use of Color requirements state:

1.4.1 Use of Color: Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. (Level A)

When submitting an incorrect form at the "GitLab import" page, the field "Project slug" has a red border around it with a tooltip attached. This is not accessible to visually impaired users as screenreaders might have problems connecting the form field with the error message tooltip. Instead, we should make use of an inline error message.