add changelog for 0.21.1 #5937

Job	Run time
build_linux (3.10)	29m 38s
build_linux (3.9)	27m 52s
build_linux (3.11)	30m 9s
build_linux (3.12)	28m 14s
build_linux (3.13)	34m 32s
build_linux (3.14)	29m 50s
build_windows (3.11)	45m 19s
build_windows (3.9)	45m 33s
build_windows (3.10)	44m 22s
build_windows (3.13)	43m 35s
build_windows (3.14)	45m 25s
build_windows (3.12)	44m 46s
test_examples_linux (3.11, false, ubuntu-22.04)	9m 31s
test_linux (3.9, false, ubuntu-22.04)	10m 44s
test_linux (3.14, false, ubuntu-22.04)	9m 38s
test_linux (3.11, false, ubuntu-22.04)	10m 10s
array-api-conformity (3.10, false, ubuntu-22.04)	5m 23s
test_linux (3.10, false, ubuntu-22.04)	10m 34s
test_linux (3.12, false, ubuntu-22.04)	10m 56s
test_linux (3.13, false, ubuntu-22.04)	11m 56s
test_windows (3.10, false, windows-latest)	15m 11s
test_windows (3.9, false, windows-latest)	16m 0s
test_windows (3.13, false, windows-latest)	14m 27s
test_windows (3.12, false, windows-latest)	15m 11s
test_windows (3.14, false, windows-latest)	15m 6s
test_windows (3.11, false, windows-latest)	13m 45s
upload_linux	0s
upload_windows	0s
Clean up anaconda packages	0s
	10h 17m 47s

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