build

Bump version: 3.9.20 → 3.9.21 #1721

Job	Run time
py38 (ubuntu)	30m 15s
check	42s
docs	58s
py39 (ubuntu)	30m 16s
py311 (ubuntu)	30m 15s
py39 (windows)	11m 13s
py310 (ubuntu)	30m 15s
py311 (windows)	13m 7s
py310 (windows)	12m 30s
py311 (macos)	7m 57s
Upload coverage to Coveralls	0s
Deploy docs to GitHub Pages	-1s
	2h 47m 27s

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