Tests

Drop support for running with Python 3.8 #14221

Job	Run time
Test mypyc suite with 32-bit Python	7m 5s
Test suite with py39-ubuntu, mypyc-compiled	18m 32s
Test suite with py39-windows-64	20m 57s
Test suite with py310-ubuntu	16m 59s
Test suite with py311-ubuntu, mypyc-compiled	16m 21s
Test suite with py312-ubuntu, mypyc-compiled	18m 29s
Test suite with py313-ubuntu, mypyc-compiled	18m 33s
mypyc runtime tests with py39-macos	4m 42s
Type check our own code (py39-ubuntu)	1m 54s
Type check our own code (py39-windows-64)	2m 19s
Formatting and code style with Black + ruff	58s
	2h 6m 49s

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