Prevent legal value selection from triggering form submit (#9831)

Use event.preventDefault to prevent the app from trying to submit the
legal values (or the strategy) form when you hit "enter" in the legal
values filter input.

frontend/src/component/common/NewConstraintAccordion/ConstraintAccordionEdit/ConstraintAccordionEditBody/RestrictiveLegalValues/RestrictiveLegalValues.tsx

@@ -159,6 +159,7 @@ export const RestrictiveLegalValues = ({
 
     const handleSearchKeyDown = (event: React.KeyboardEvent) => {
         if (event.key === 'Enter' && filteredValues.length > 0) {
+            event.preventDefault();
             const firstValue = filteredValues[0].value;
             onChange(firstValue);
         }