Fix oauth2 error handle not return immediately (#32514) (#32516)

Backport #32514 by lunny

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/auth/oauth.go

@@ -953,6 +953,8 @@ func SignInOAuthCallback(ctx *context.Context) {
 		}
 		if err, ok := err.(*go_oauth2.RetrieveError); ok {
 			ctx.Flash.Error("OAuth2 RetrieveError: "+err.Error(), true)
+			ctx.Redirect(setting.AppSubURL + "/user/login")
+			return
 		}
 		ctx.ServerError("UserSignIn", err)
 		return