Add Python 3.11 support #72

Job	Run time
build (Python 3.8, Django 2.2)	34s
build (Python 3.8, Django 3.2)	28s
build (Python 3.8, Django 4.0)	31s
build (Python 3.8, Django 4.1)	29s
build (Python 3.8, Django 4.2)	27s
build (Python 3.9, Django 2.2)	27s
build (Python 3.9, Django 3.2)	27s
build (Python 3.9, Django 4.0)	31s
build (Python 3.9, Django 4.1)	23s
build (Python 3.9, Django 4.2)	23s
build (Python 3.10, Django 3.2)	34s
build (Python 3.10, Django 4.0)	32s
build (Python 3.10, Django 4.1)	29s
build (Python 3.10, Django 4.2)	28s
build (Python 3.11, Django 3.2)	31s
build (Python 3.11, Django 4.0)	30s
build (Python 3.11, Django 4.1)	32s
build (Python 3.11, Django 4.2)	24s
build (Python pypy-3.10, Django 2.2)	53s
build (Python pypy-3.10, Django 3.2)	49s
build (Python pypy-3.10, Django 4.0)	45s
build (Python pypy-3.10, Django 4.1)	43s
build (Python pypy-3.10, Django 4.2)	48s
build (Python 3.11, Django qa)	41s
build (Python 3.10, Django main)	47s
build (Python 3.11, Django main)	33s
build (Python pypy-3.10, Django main)	1m 15s
	15m 54s

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