Update where ConnectionDoesNotExist is imported from

[mthuurne]

Problem

ConnectionDoesNotExist does not exist in django.db.utils in django-stubs, as it was moved to django.utils.connection in Django 3.2. At some point in the future, I expect it will also only be available from its new location in Django itself.

Solution

Import it from its new location.

Commandments

• Write PEP8 compliant code.
• Cover it with tests.
• Update CHANGES.rst file to describe the changes, and quote according issue with GH-<issue_number>.
• Pay attention to backward compatibility, or if it breaks it, explain why.
• Update documentation (if relevant).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.56%. Comparing base (7b8a58b) to head (a1530ad).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #566   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files           6        6           
  Lines         768      768           
=======================================
  Hits          757      757           
  Misses         11       11           

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[foarsitter]

Thanks @mthuurne