Unmount React tree automatically in tests

Summary: In the next diff, tests started to fail suddenly, probably as side effect of a changed module loading order or smthg, and started showing DOMs of different tests in test results. Figured that testing-library/react + jest doesn't automatically doesn't clean up the DOM as I hoped it would

Reviewed By: timur-valiev

Differential Revision: D32463402

fbshipit-source-id: 48d26badf774482e7320632e486dfc6358946484

desktop/scripts/jest-setup-after.js

@@ -8,6 +8,7 @@
  */
 
 // jest-setup-after will run after Jest has been initialized, so that it can be adapted.
+import {cleanup} from '@testing-library/react';
 
 const test = global.test;
 if (!test) {
@@ -31,3 +32,5 @@ test.unix = function local() {
   // eslint-disable-next-line
   return fn.apply(null, arguments);
 };
+
+afterEach(cleanup);