docs: Update an import in best-practice.md (#573)

There's no `should` export in bun:test, the correct import should be `expect`

Author: RyanGst

docs/essential/best-practice.md

@@ -230,7 +230,7 @@ You can test your controller using `handle` to directly call a function (and it'
 import { Elysia } from 'elysia'
 import { Service } from './service'
 
-import { describe, it, should } from 'bun:test'
+import { describe, it, expect } from 'bun:test'
 
 const app = new Elysia()
     .get('/', ({ stuff }) => {