Update 2022-03-08-react-18-upgrade-guide.md (#5208)

Author: claidler

content/blog/2022-03-08-react-18-upgrade-guide.md

@@ -259,7 +259,7 @@ You can also set the flag to `false` to tell React that `act` isn't needed. This
 
 Eventually, we expect testing libraries will configure this for you automatically. For example, the [next version of React Testing Library has built-in support for React 18](https://github.com/testing-library/react-testing-library/issues/509#issuecomment-917989936) without any additional configuration.
 
-[More background on the the `act` testing API and related changes](https://github.com/reactwg/react-18/discussions/102) is available in the working group.
+[More background on the `act` testing API and related changes](https://github.com/reactwg/react-18/discussions/102) is available in the working group.
 
 ## Dropping Support for Internet Explorer {#dropping-support-for-internet-explorer}