Update webhook.rst

Co-authored-by: Oskar Stark <[email protected]>

Author: TimoBakx

webhook.rst

@@ -89,7 +89,7 @@ Sendgrid        ``mailer.webhook.request_parser.sendgrid``
 
 .. versionadded:: 6.4
 
-    Webhook support for the Sendgrid service was introduced in Symfony 6.4
+    Webhook support for the Sendgrid service was introduced in Symfony 6.4.
 
 
 Set up the webhook in the third-party mailer. For Mailgun, you can do this