Fix unclosed files in download.py, test_onnxifi.py, test_trt.py (#18017)
Summary:
According to https://docs.python.org/3/tutorial/inputoutput.html, it is good practice to use the "with" keyword when dealing with file objects. If not, you should call f.close() to close the file and immediately free up any system resources used by it. Thus, I adjust the open file function to "with open() as f".
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18017
Differential Revision: D14475112
Pulled By: ezyang
fbshipit-source-id: d1c0821e39cb8a09f86d6d08b437b4a99746416c
