Fix #134708: Audio render does not change file extension

Caused by case sensitive string comparison between RNA enum
name and pre-defined array with extensions.

The array with extensions was also missing ".aac" string.

Pull Request: https://projects.blender.org/blender/blender/pulls/134761

source/blender/editors/sound/sound_ops.cc

@@ -431,6 +431,7 @@ static const char *snd_ext_sound[] = {
     ".mp3",
     ".ogg",
     ".wav",
+    ".aac",
     nullptr,
 };
 
@@ -445,7 +446,7 @@ static bool sound_mixdown_check(bContext * /*C*/, wmOperator *op)
     if (item->value == container) {
       const char **ext = snd_ext_sound;
       while (*ext != nullptr) {
-        if (STREQ(*ext + 1, item->name)) {
+        if (STRCASEEQ(*ext + 1, item->name)) {
           extension = *ext;
           break;
         }