Flake8/pyflakes needs to update to work with Python 3.8

Today on DM-28314 I used the python walrus operator and flake8/pyflakes broke completely. It turns out that we need to update our flake8 packages so that we can make use of python 3.8 features. An initial plan would be:

• Update the dependencies used by pull requests to update them to current flake8/pyflakes versions.

• Update the GH Action files to use python 3.8.

• Fix any packages where that pull request fails because of a flake8 problem

Once this is done then the next step is to update the rubin-env flake8 version but that should be straightforward if we know that the GitHub pull requests are working.