fix: SelectAccount was not well displayed

Since the SelectBox is within the Title, but the title
is not very height, the box was not displayed correctly.

We use the `fixed` props in order to be created outside
of the Title flow.

packages/cozy-harvest-lib/src/components/AccountSelectBox/AccountSelectBox.jsx

@@ -22,6 +22,7 @@ const AccountSelectBox = ({
   }
   return (
     <SelectBox
+      menuPosition="fixed"
       size="tiny"
       options={accountsAndTriggers}
       onChange={onChange}