Revert "Cleanup: quiet const cast warning"

This reverts commit 626fb290eb.

This was an intentional change for FFMPEG v5.0,
removing the cast should be done in a version check instead.

source/blender/blenkernel/intern/writeffmpeg.c

@@ -869,7 +869,7 @@ static int start_ffmpeg_impl(FFMpegContext *context,
 {
   /* Handle to the output file */
   AVFormatContext *of;
-  AVOutputFormat *fmt;
+  const AVOutputFormat *fmt;
   char name[FILE_MAX], error[1024];
   const char **exts;