add changelog for 0.21.1 #5938

Job	Run time
build_windows (3.11)	48m 23s
build_windows (3.14)	42m 35s
build_windows (3.13)	44m 14s
build_linux (3.9)	29m 55s
build_linux (3.11)	29m 58s
build_linux (3.13)	31m 7s
build_linux (3.14)	29m 0s
build_windows (3.12)	44m 20s
build_windows (3.10)	45m 25s
build_linux (3.10)	30m 36s
build_linux (3.12)	31m 6s
build_windows (3.9)	44m 54s
test_examples_linux (3.11, false, ubuntu-22.04)	9m 0s
test_linux (3.9, false, ubuntu-22.04)	10m 20s
test_linux (3.12, false, ubuntu-22.04)	10m 54s
test_linux (3.11, false, ubuntu-22.04)	10m 10s
test_linux (3.10, false, ubuntu-22.04)	10m 48s
test_linux (3.13, false, ubuntu-22.04)	10m 56s
test_linux (3.14, false, ubuntu-22.04)	10m 27s
array-api-conformity (3.10, false, ubuntu-22.04)	6m 9s
upload_linux	0s
test_windows (3.11, false, windows-latest)	14m 58s
test_windows (3.9, false, windows-latest)	15m 16s
test_windows (3.14, false, windows-latest)	15m 31s
test_windows (3.10, false, windows-latest)	13m 38s
test_windows (3.12, false, windows-latest)	15m 2s
test_windows (3.13, false, windows-latest)	14m 33s
upload_windows	0s
Clean up anaconda packages	0s
	10h 19m 15s

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