Fix grammatical error: remove unnecessary 'a' in 03-server-actions-an…

…d-mutations.mdx (#72496)

#### Description:
- fix grammatical error: remove unnecessary 'a'

Co-authored-by: Delba de Oliveira <32464864+delbaoliveira@users.noreply.github.com>

docs/01-app/02-building-your-application/02-data-fetching/03-server-actions-and-mutations.mdx

@@ -856,7 +856,7 @@ See [additional examples](/docs/app/api-reference/functions/cookies#deleting-coo
 ## Security
 
 By default, when a Server Action is created and exported, it creates a public HTTP endpoint
-and should be treated with the same security assumptions and authorization checks. This means, even if a Server Action or utility function is not imported elsewhere in your code, it’s still a publicly accessible.
+and should be treated with the same security assumptions and authorization checks. This means, even if a Server Action or utility function is not imported elsewhere in your code, it’s still publicly accessible.
 
 To improve security, Next.js has the following built-in features: