change aria-disabled on form buttons to disabled (vercel#63852)

- aria-disabled does not disable the button

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Co-authored-by: JJ Kasper <jj@jjsweb.site>

Author: vespertilian

docs/02-app/01-building-your-application/02-data-fetching/02-server-actions-and-mutations.mdx

@@ -243,7 +243,7 @@ export function SubmitButton() {
   const { pending } = useFormStatus()
 
   return (
-    <button type="submit" aria-disabled={pending}>
+    <button type="submit" disabled={pending}>
       Add
     </button>
   )
@@ -259,7 +259,7 @@ export function SubmitButton() {
   const { pending } = useFormStatus()
 
   return (
-    <button type="submit" aria-disabled={pending}>
+    <button type="submit" disabled={pending}>
       Add
     </button>
   )