Change to using arrow functions (#1603)

* Change to using arrow functions

Co-authored-by: v1b3m <vibenjamin6@gmail.com>
Co-authored-by: Matheus <matheus_benini@hotmail.com>

* Add lint rule

---------

Co-authored-by: v1b3m <vibenjamin6@gmail.com>
Co-authored-by: Matheus <matheus_benini@hotmail.com>
Co-authored-by: Charles Bochet <charles@twenty.com>

front/src/testing/sleep.ts

@@ -1,5 +1,4 @@
-export async function sleep(ms: number) {
-  return new Promise((resolve) => {
+export const sleep = async (ms: number) =>
+  new Promise((resolve) => {
     setTimeout(resolve, ms);
   });
-}