Context manager open(file) as f fixes (#7289)

* Flask context manager `open()` fix

* Additional read context manager fixes

utils/flask_rest_api/restapi.py

@@ -1,6 +1,8 @@
+# YOLOv5 🚀 by Ultralytics, GPL-3.0 license
 """
 Run a Flask REST API exposing a YOLOv5s model
 """
+
 import argparse
 import io