docs: Renamed function that is used by other name (#56170)
In "app/actions.ts" the function is named like create(), but in "app/add-form.tsx" file "createTodo" function is imported and used. This is related to TypeScript examples, .js files are ok.
### What?
Renamed a function.
### Why?
There are two example files in docs ([Error Handling](https://nextjs.org/docs/app/building-your-application/data-fetching/forms-and-mutations#error-handling) section) and the `app/add-form.tsx` is importing function `create` from `app/actions.ts` by another name (`createTodo`).
### How?
Fixed by renaming function to `createTodo`, to match .js file with the same example.
