UI: Opus files not included in sound files filter

Include `.opus` extension in audio filter list

Fixes #118235

Pull Request: https://projects.blender.org/blender/blender/pulls/118238

source/blender/imbuf/intern/util.cc

@@ -86,6 +86,7 @@ const char *imb_ext_audio[] = {
     ".aiff",
     ".m4a",
     ".mka",
+    ".opus",
     nullptr,
 };