Redact the event before verifying its signature

... in the federation invite API.

src/github.com/matrix-org/dendrite/federationapi/writers/invite.go

@@ -73,7 +73,7 @@ func Invite(
 	// Check that the event is signed by the server sending the request.
 	verifyRequests := []gomatrixserverlib.VerifyJSONRequest{{
 		ServerName: event.Origin(),
-		Message:    event.JSON(),
+		Message:    event.Redact().JSON(),
 		AtTS:       event.OriginServerTS(),
 	}}
 	verifyResults, err := keys.VerifyJSONs(verifyRequests)