Tests

Improve CallableType join in simple cases (#18406) #20206

Job	Run time
Test mypyc suite with 32-bit Python	9m 31s
Test suite with py314-ubuntu, mypyc-compiled	15m 1s
Test suite with py313-ubuntu, mypyc-compiled	14m 59s
Test suite with py312-ubuntu	10m 14s
Test suite with py311-ubuntu	9m 50s
Test suite with py314t-ubuntu, mypyc-compiled	17m 46s
Test suite with py310-ubuntu, mypyc-compiled	15m 29s
mypyc runtime tests with py313-macos	6m 4s
Formatting and code style with Black + ruff	1m 56s
Type check our own code (py310-ubuntu)	1m 43s
Parallel tests with py314-ubuntu, interpreted	24m 6s
Parallel tests with py314-ubuntu, mypyc-compiled	28m 48s
mypyc runtime tests with py310-ubuntu	5m 36s
Test suite with py314-windows-64	25m 48s
Type check our own code (py310-windows-64)	2m 17s
	3h 9m 8s

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