update all required dependencies to support react 18.

react 18 forces to explicitly name the `children` attribute so let's update
components and hooks.

most of the tests broke due to the changes induced by the new rendering
behavior of react 18 and react-query v4, so we changed the approach
that we had with tests to an approach more based on `waitFor` in order
to have tests the most render-agnostic as possible.

This bug was occuring when clicking on the button "Login to purchase"
causing a removal of existing react-query queries. This was caused by
premature removal of the pending useCourse query which was never notified
that it had been removed during its loading, resulting in an infinite
loading state.