Fixed enter submitting form in dropdown

## What does this MR do?

When searching for a branch in the ref switcher & then pressing enter it would submit the form without anything. This instead doesn't submit the form without anything being selected in the dropdown.

Also improved the UX by making it submit with `Turoblinks` as currently no loading bar is shown so the user has no idea if anything is happening.

## What are the relevant issue numbers?

Closes #19549 

See merge request !5111