[Typo]: A slight typo in Server Functions docs.

[TheCaptain1810]

Summary

Link for md: https://github.com/reactjs/react.dev/blob/main/src/content/reference/rsc/server-functions.md

I know it's not a great deal, but I'll fix this shortly.

Page

https://react.dev/reference/rsc/server-functions

Details

It should be "When a Server Function is" instead of "When a Server Functions is", since it's in singular form.