Tests

Add --disallow-str-iteration flag #20130

Job	Run time
Test suite with py313-ubuntu, mypyc-compiled	14m 45s
Parallel tests with py314-ubuntu, mypyc-compiled	29m 5s
Test suite with py312-ubuntu	9m 58s
Test suite with py314-windows-64	26m 49s
Test suite with py314t-ubuntu, mypyc-compiled	17m 2s
mypyc runtime tests with py310-ubuntu	5m 35s
Type check our own code (py310-ubuntu)	1m 41s
mypyc runtime tests with py313-macos	6m 44s
Test suite with py310-ubuntu, mypyc-compiled	15m 8s
Type check our own code (py310-windows-64)	2m 37s
Formatting and code style with Black + ruff	1m 56s
Parallel tests with py314-ubuntu, interpreted	24m 44s
Test suite with py314-ubuntu, mypyc-compiled	14m 31s
Test suite with py311-ubuntu	9m 27s
Test mypyc suite with 32-bit Python	9m 32s
	3h 9m 34s

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