Update index.mdx (#64794)

Removed a type annotation from a code block

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docs/02-app/01-building-your-application/09-authentication/index.mdx

@@ -159,7 +159,7 @@ To prevent unnecessary calls to your authentication provider's API or database,
 ```ts filename="app/actions/auth.ts" switcher
 import { SignupFormSchema, FormState } from '@/app/lib/definitions'
 
-export async function signup(state: FormState, formData: FormData) {
+export async function signup(state: FormState, formData) {
   // Validate form fields
   const validatedFields = SignupFormSchema.safeParse({
     name: formData.get('name'),