SDL_mixer: update vendored opus

From d58c0ff225b6d78be063655182cc2ab851e04bf3 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Fri, 27 Oct 2023 11:30:32 +0300
Subject: [PATCH] update vendored opus

---
 external/opus | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/external/opus b/external/opus
index d639dbba..71e9d9b1 160000
--- a/external/opus
+++ b/external/opus
@@ -1 +1 @@
-Subproject commit d639dbbaa388ebdc792326f78fce780e250b4a70
+Subproject commit 71e9d9b1026a37715556f9d5efa7c56ffacb6b88