docs: update app secrets docs (#30859)

Co-authored-by: Rhys Arkins <rhys@arkins.net>
Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>

docs/usage/mend-hosted/app-secrets.md

@@ -37,7 +37,7 @@ To add a secret for the Mend cloud app:
      "hostRules": [
        {
          "matchHost": "github.com",
-         "token": "{{ secrets.MY-ORG-SECRET-1 }}"
+         "token": "{{ secrets.MY_ORG_SECRET }}"
        }
      ]
    }