docs: fix jest.config.js to use correct target (#12999)

www/apps/book/app/learn/debugging-and-testing/testing-tools/page.mdx

@@ -41,6 +41,7 @@ module.exports = {
       {
         jsc: {
           parser: { syntax: "typescript", decorators: true },
+          target: "es2021"
         },
       },
     ],