add opus, oga extensions

add `.opus` and `.oga` extensions for mime type `audio/ogg`

Reference:
- https://wiki.xiph.org/MIME_Types_and_File_Extensions#.opus_-_audio/ogg

pyglossary/plugins/aard2_slob/writer.py

@@ -56,6 +56,8 @@ class Writer:
 		"otf": "application/x-font-opentype",
 		"mp3": "audio/mpeg",
 		"ogg": "audio/ogg",
+		"opus": "audio/ogg",
+		"oga": "audio/ogg",
 		"spx": "audio/x-speex",
 		"wav": "audio/wav",
 		"ini": "text/plain",