Update react-testing-library

[scurker]

We're currently "stuck" on react testing library v12, because versions 13+ have removed support for React v16 and below:

React Testing Library versions 13+ require React v18. If your project uses an older version of React, be sure to install version 12:

This means we can't take advantage of any new queries/matchers that get added to react-testing-library/dom due to the following issues:

• Type conflicts in testing-library vs react testing-library/react-testing-library#1184
• @testing-library/dom should be a peer dependency testing-library/react-testing-library#1103

If any of the above issues get resolved, it might be possible for us to install the dom library as a peer dependency to take advantage of any new features OR if we fully migrate away from enzyme in order to upgrade to react 17+.

[scurker]

This depends on #1473