Merge pull request #28789 from qhua948/fix-typo-adminnsion-controllers

Fixed up typo in extensible-admission-controllers.md

Author: k8s-ci-robot

content/en/docs/reference/access-authn-authz/extensible-admission-controllers.md

@@ -282,7 +282,7 @@ Of course you need to set up the webhook server to handle these authentications.
 
 ### Request
 
-Webhooks are sent a POST request, with `Content-Type: application/json`,
+Webhooks are sent as POST requests, with `Content-Type: application/json`,
 with an `AdmissionReview` API object in the `admission.k8s.io` API group
 serialized to JSON as the body.