Fix type narrowing in lambda expressions #11495

Job	Run time
Test mypyc suite with 32-bit Python	8m 12s
Test suite with py38-ubuntu, mypyc-compiled	22m 42s
Test suite with py38-windows-64	38m 12s
Test suite with py39-ubuntu	19m 12s
Test suite with py310-ubuntu	23m 59s
Test suite with py311-ubuntu, mypyc-compiled	19m 50s
Test suite with py312-ubuntu, mypyc-compiled	26m 12s
mypyc runtime tests with py39-macos	4m 38s
mypyc runtime tests with py38-debug-build-ubuntu	6m 42s
Type check our own code (py38-ubuntu)	2m 15s
Type check our own code (py38-windows-64)	3m 1s
Formatting and code style with Black + ruff	50s
	2h 55m 45s

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