Add Django 4.2 to test matrix and classifiers #401

Job	Run time
Check for news fragments in 'changelog.d/'	11s
Lint (black)	32s
Lint (flake8)	22s
Lint (isort)	25s
Lint (mypy)	41s
Test Python 3.8, Django 3.2, Redis.py latest	4m 29s
Test Python 3.8, Django 4.0, Redis.py latest	4m 16s
Test Python 3.8, Django 4.1, Redis.py latest	4m 17s
Test Python 3.8, Django 4.2, Redis.py latest	4m 16s
Test Python 3.9, Django 3.2, Redis.py latest	4m 29s
Test Python 3.9, Django 4.0, Redis.py latest	4m 24s
Test Python 3.9, Django 4.1, Redis.py latest	4m 16s
Test Python 3.9, Django 4.2, Redis.py latest	4m 31s
Test Python 3.10, Django 3.2, Redis.py latest	4m 17s
Test Python 3.10, Django 4.0, Redis.py latest	4m 26s
Test Python 3.10, Django 4.1, Redis.py latest	4m 24s
Test Python 3.10, Django 4.2, Redis.py latest	4m 36s
Test Python 3.6, Django 3.2, Redis.py latest	4m 32s
Test Python 3.7, Django 3.2, Redis.py latest	4m 22s
Test Python 3.11, Django 4.1, Redis.py latest	4m 17s
Test Python 3.11, Django 4.2, Redis.py latest	4m 28s
Test Python 3.11, Django 4.2, Redis.py master	4m 16s
Test Python 3.11, Django main, Redis.py latest	4m 25s
Test Python 3.11, Django main, Redis.py master	4m 22s
	1h 25m 34s

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