Update changelog for 1.9 with acknowledgements. (#16989) #421

Job	Run time
Test mypyc suite with 32-bit Python	8m 0s
Test suite with py38-ubuntu, mypyc-compiled	21m 49s
Test suite with py38-windows-64	26m 16s
Test suite with py39-ubuntu	18m 41s
Test suite with py310-ubuntu	17m 54s
Test suite with py311-ubuntu, mypyc-compiled	17m 40s
Test suite with py312-ubuntu, mypyc-compiled	19m 48s
mypyc runtime tests with py39-macos	9m 8s
mypyc runtime tests with py38-debug-build-ubuntu	5m 30s
Type check our own code (py38-ubuntu)	1m 49s
Type check our own code (py38-windows-64)	2m 36s
Formatting and code style with Black + ruff	39s
	2h 29m 50s

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