We forgot to change the line rendering the image in commits 3574bf867c
and 810bdae37a, and so the custom image was being ignored.
Note that, in the test, we're stubbing a constant instead of adding a
new image. The main reason is that, if we add a new image, forks would
have to change the image when they change the `VALID_IMAGES` constant;
otherwise the tests would fail.
As mentioned in commit 5214d89c8, there are several issues with
submitting a form when a `<select>` tag changes. In particular, keyboard
users might accidentally fire the event while browsing the options, and
screen reader users will find a form with no obvious way to submit it.
In this case, there's an extra problem: in commit be8a0dbe8 we added a
second `<select>` field to this form, which also submitted on change.
Sometimes users changed one of the values and wanted to change the other
value as well before submitting the form. However, it wasn't possible,
because we would submit it before they had a chance to change the second
value.
So now we don't submit the form on change and add a submit button. This
is similar to what we do in the "Advanced filters" we use in several
places.
