chore: Drop support for Django 3.2, 4.0, 4.1

[JuroOravec]

While I was hacking away at tests for https://github.com/EmilStenstrom/django-components/issues/436, I had some strange error with Django 3.2. That got me searching, and along the way, I stumbled across the Django download page, which says that Django 3.2, 4.0, and 4.1 are no longer supported.

Support policy was recently discussed in https://github.com/EmilStenstrom/django-components/issues/418#issuecomment-2028479587, based on which I think we can drop these versions.

One other thing I noticed was that the supported_versions script still included v3.2-4.2 in the generated text. This is because it took the data from the table at https://docs.djangoproject.com/en/dev/faq/install/, which lists even unsupported Django versions. So instead I updated the script to fetch the data from the table at https://www.djangoproject.com/download/, which includes only supported versions.

[EmilStenstrom]

Great find! Makes sense.

[JuroOravec]

@EmilStenstrom Good idea! I'll be using some TestCase subclass for https://github.com/EmilStenstrom/django-components/issues/436, so I've kept an empty subclass there and renamed it to BaseTestCase. See https://github.com/EmilStenstrom/django-components/pull/443/commits/eb40afba7b55a5649a380cc80ba3b99bf1b6ba16