[MAINT] Add development stub after 0.20.0 release #5612

Job	Run time
build_linux (3.9)	36m 41s
build_linux (3.10)	36m 24s
build_linux (3.11)	35m 55s
build_windows (3.9)	57m 27s
build_linux (3.12)	35m 49s
build_windows (3.10)	58m 48s
build_linux (3.13)	36m 16s
build_windows (3.11)	56m 7s
build_windows (3.12)	56m 7s
build_windows (3.13)	55m 14s
array-api-conformity (3.10, false, ubuntu-22.04)	5m 14s
test_examples_linux (3.11, false, ubuntu-22.04)	8m 11s
test_linux (3.9, false, ubuntu-22.04)	10m 53s
test_linux (3.10, false, ubuntu-22.04)	11m 34s
test_linux (3.11, false, ubuntu-22.04)	10m 36s
test_linux (3.12, false, ubuntu-22.04)	10m 37s
test_linux (3.13, false, ubuntu-22.04)	11m 31s
upload_linux	0s
test_windows (3.9, false, windows-2019)	13m 7s
test_windows (3.10, false, windows-2019)	13m 4s
test_windows (3.11, false, windows-2019)	13m 0s
test_windows (3.12, false, windows-2019)	13m 1s
test_windows (3.13, false, windows-2019)	13m 41s
upload_windows	0s
Clean up anaconda packages	0s
	9h 59m 17s

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