This way the relationship between the two elements is more obvious. And
since now the button and the form are siblings, it's easier to find one
based on the other using CSS or JavaScript.
A button cannot be inside an anchor tag, and it might confuse some
browsers or screen readers.
We're also making it clear in the tests that the intention is to use a
button there by using `click_button` instead of `click_on` since the
latter also clicks on links.
