use context manager for path extension in torch.hub (#75786)
We are using the idiom
```py
sys.path.insert(0, path)
# do something
sys.path.remove(path)
```
three times in `torch.hub`. This is a textbook case for using a context manager. In addition, by using `try` / `finally` we can enforce the Python path is back in its original state even if the actual action raises an exception:
```py
import sys
path = "/tmp"
# PR
try:
sys.path.insert(0, path)
try:
# Any exception raised while performing the actual functionality
raise Exception
finally:
sys.path.remove(path)
except Exception:
assert path not in sys.path
# main
try:
sys.path.insert(0, path)
# Any exception raised while performing the actual functionality
raise Exception
sys.path.remove(path)
except Exception:
assert path in sys.path
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75786
Approved by: https://github.com/NicolasHug
