Bump actions/checkout from 3.6.0 to 4.0.0 #424

Job	Run time
Python 3.6 on macOS	5m 3s
Python 3.11 on macOS	4m 26s
Python 3.11 (minimal build) on macOS	4m 29s
Linux docs	1m 37s
Linux meta	1m 46s
Linux mypy	1m 51s
Linux pypy	3m 34s
Linux py36	1m 59s
Linux py37	2m 41s
Linux py38	1m 58s
Linux py39	2m 8s
Linux py310	1m 56s
Linux py311	2m 25s
Linux py311 system	2m 24s
Linux py311 minimal	2m 17s
Python 3.6 on Windows x86	3m 39s
Python 3.7 on Windows x86	3m 27s
Python 3.8 on Windows x86	3m 31s
Python 3.9 on Windows x86	5m 23s
Python 3.10 on Windows x86	3m 52s
Python 3.11 on Windows x86	3m 4s
Python 3.6 on Windows x64	3m 18s
Python 3.7 on Windows x64	2m 16s
Python 3.8 on Windows x64	2m 45s
Python 3.9 on Windows x64	2m 54s
Python 3.10 on Windows x64	3m 21s
Python 3.11 on Windows x64	2m 53s
	1h 20m 57s

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