Code formatting issue with latest flake8


https://github.com/pytorch/ignite/runs/7781175697?check_suite_focus=true#step:11:84

```
Collecting flake8
  Downloading flake8-5.0.4-py2.py3-none-any.whl (61 kB)

+ flake8 ignite tests examples --config setup.cfg
ignite/metrics/psnr.py:12:121: E501 line too long (121 > 120 characters)
```