[FIX] web: Make accessible with keyboard the delete button on o2m fields (#23719)

* [FIX] web: Make accessible with keyboard the delete button on o2m fields

Currently, the delete button in one2many fields (trash icon) is not
reachable when using the keyboard, because it's neither a link, nor a
button or any other interactable HTML element, but a `<span>`.

This change causes that button to be an actual HTML button keeping the
same appearance, so it may be reached when using the keyboard.

* [FIX] web: Modify test to expect button instead of span as o2m trash icon

Since buttons to delete records in o2m fields (the trash icon) were
changed from `<span>` to `<button>` to be able to access them with the
keyboard, the test need to be modified so it expect the new element
type and doesn't break.