SDL_mixer: upgrade vendored opus to latest v1.4 release.

From 3c7074d47416cd0f0a425b7322aa205f838384f9 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Tue, 25 Apr 2023 18:55:56 +0300
Subject: [PATCH] upgrade vendored opus to latest v1.4 release.

Closes https://github.com/libsdl-org/SDL_mixer/issues/513.
---
 .gitmodules   | 2 +-
 external/opus | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.gitmodules b/.gitmodules
index 6ec6b106..ee7bd10e 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -13,7 +13,7 @@
 [submodule "external/opus"]
 	path = external/opus
 	url = https://github.com/libsdl-org/opus.git
-	branch = v1.3.1-SDL
+	branch = v1.4-SDL
 [submodule "external/opusfile"]
 	path = external/opusfile
 	url = https://github.com/libsdl-org/opusfile.git
diff --git a/external/opus b/external/opus
index 3ab0bb04..940c94b1 160000
--- a/external/opus
+++ b/external/opus
@@ -1 +1 @@
-Subproject commit 3ab0bb045e3dbd1ecb66962b0bf8eb548cf5287c
+Subproject commit 940c94b1ab2d9a953cb76f6cede7a279b48b656d