Deprecate Django < 4.2, Python < 3.10 and fix old mock paths

[tm-kn]

A little tidy up after #50.

• A few tox.ini updates so the test dependencies are installed more consistently. There were some issues with the setup installing the wrong versions of dependencies.
• Added a broken mock for the urlopen path for the Wagtail's urlopen import.
• Deprecate Django less than 4.2 in the setup.cfg.
• Deprecate Python 3.8 and 3.9 due to issues with boto3 resolving dependencies.

[zerolab]

This works.

I added a note and a non-blocking suggestion

[zerolab]

There's something funny with py 3.8/3.9. It errors with django.core.exceptions.ImproperlyConfigured: Could not load Boto3's S3 bindings. No module named 's3transfer.constants'

it loads boto==2.49.0,boto3==1.7.84,botocore==1.10.84,s3transfer==0.1.13

boto3 is at 1.35.x
s3transfer at 0.10.x

upd: on 3.10 it loads "boto3==1.35.20,botocore==1.35.20,s3transfer==0.10.2"

I suggest dropping Python 3.8 as support for it ends in a month - https://endoflife.date/python, and bump min s3transfer and or boto3 versions in testing

[tm-kn]

@zerolab Yeah, have been wrangling with this... It seems the easiest way is to drop 3.8 and 3.9. Looks like boto3 moves fast... No one would want to be on modern Django, Wagtail, and old Python. I'd rather not release a broken package to the world.

[zerolab]

One small detail and this is good to go!

Nice one on requiring a minimum of Python 3.10 💪🏼

[tm-kn]

it seems that it's urllib3 dependency breaking 3.8 and 3.9.