Ensure that FD 3 gets closed

It appears that Python doesn't reliably (or maybe just doesn't at all) flush and close non-standard FDs on exit. This randomly caused the artefacts list to get lost to /dev/null.

codearchiver/cli.py

@@ -206,8 +206,9 @@ def main():
 		if args.writeArtefactsFd3:
 			with storage.lock():
 				artefacts = storage.list_new_files()
-			for filename in artefacts:
-				print(filename, file = artefactsFd)
+			with artefactsFd:
+				for filename in artefacts:
+					print(filename, file = artefactsFd)
 
 if __name__ == '__main__':
 	main()