Bump actions/setup-python from 2 to 4 #525

Job	Run time
Test Python 3.8, Django 4.1, Redis.py latest	4m 59s
Test Python 3.8, Django 4.2, Redis.py latest	4m 45s
Test Python 3.9, Django 4.1, Redis.py latest	4m 49s
Test Python 3.9, Django 4.2, Redis.py latest	4m 34s
Test Python 3.10, Django 4.1, Redis.py latest	4m 44s
Test Python 3.10, Django 4.2, Redis.py latest	4m 35s
Test Python 3.11, Django 4.1, Redis.py latest	4m 36s
Test Python 3.11, Django 4.2, Redis.py latest	4m 31s
Test Python 3.11, Django 4.2, Redis.py master	4m 29s
Check for news fragments in 'changelog.d/'	19s
Test Python 3.11, Django main, Redis.py latest	4m 42s
Test Python 3.11, Django main, Redis.py master	4m 44s
Lint (black)	39s
Lint (ruff)	21s
Lint (mypy)	31s
	53m 18s

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