Add 0.20.0 changes to CHANGELOG.md #5604

Job	Run time
build_linux (3.9)	37m 21s
build_linux (3.10)	36m 31s
build_windows (3.9)	56m 15s
build_linux (3.11)	35m 33s
build_windows (3.10)	55m 50s
build_linux (3.12)	36m 30s
build_windows (3.11)	58m 42s
build_linux (3.13)	36m 10s
build_windows (3.12)	56m 11s
build_windows (3.13)	58m 26s
test_examples_linux (3.11, false, ubuntu-22.04)	7m 17s
array-api-conformity (3.10, false, ubuntu-22.04)	4m 50s
test_linux (3.9, false, ubuntu-22.04)	10m 45s
test_linux (3.10, false, ubuntu-22.04)	10m 57s
test_linux (3.11, false, ubuntu-22.04)	10m 43s
test_linux (3.12, false, ubuntu-22.04)	10m 50s
test_linux (3.13, false, ubuntu-22.04)	10m 47s
upload_linux	0s
test_windows (3.9, false, windows-2019)	13m 46s
test_windows (3.10, false, windows-2019)	12m 33s
test_windows (3.11, false, windows-2019)	12m 44s
test_windows (3.12, false, windows-2019)	13m 9s
test_windows (3.13, false, windows-2019)	13m 26s
upload_windows	0s
Clean up anaconda packages	0s
	9h 59m 16s

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