Update test server on Python Anywhere

[mondus]

Your account "rsesheffield" uses a system image called "earlgrey" to run
your code. In one year's time, "earlgrey" will no longer be available
and your account will be switched to a newer system image. This is likely to
require changes to your code, as otherwise it will no longer run. You can
update the system image now, at a time that you control, and find out if your
code needs any changes to keep working.

The system image is essentially the version of the underlying operating
system -- it determines which system libraries you have available, which
versions of Python, and which pre-installed Python packages. "earlgrey" was
released a very long time ago, and is based on Ubuntu 16.04, with support for
Python versions up to 3.7. Our most recent system image, "haggis", is
based on 20.04 with Python supported up to 3.10, and of course all of the pre-
installed libraries like Django and Flask are much more recent too.

You can change your system image to a new one (and back again) at any time,
without any risk to your own files or data -- however, because newer system
images have newer versions of everything, your code might need modification to
run with the new system image (that's why we don't silently upgrade you in the
background when we release a new system image -- we don't want to break your
code if it's working).

This help page has all of the details about changing your system image:

https://help.pythonanywhere.com/pages/ChangingSystemImage