tests: prefer ffprobe -show_entries to -show_format_entry

The latter option was deprecated.

tests/fate-run.sh

@@ -71,7 +71,7 @@ run(){
 }
 
 probefmt(){
-    run ffprobe -show_format_entry format_name -print_format default=nw=1:nk=1 -v 0 "$@"
+    run ffprobe -show_entries format=format_name -print_format default=nw=1:nk=1 -v 0 "$@"
 }
 
 ffmpeg(){