Fix missing type store for overloads #11918

Job	Run time
Test mypyc suite with 32-bit Python	8m 14s
Test suite with py38-ubuntu, mypyc-compiled	20m 7s
Test suite with py38-windows-64	26m 34s
Test suite with py39-ubuntu	18m 26s
Test suite with py310-ubuntu	17m 48s
Test suite with py311-ubuntu, mypyc-compiled	17m 20s
Test suite with py312-ubuntu, mypyc-compiled	19m 54s
mypyc runtime tests with py39-macos	4m 42s
mypyc runtime tests with py38-debug-build-ubuntu	5m 18s
Type check our own code (py38-ubuntu)	1m 46s
Type check our own code (py38-windows-64)	2m 26s
Formatting and code style with Black + ruff	2m 14s
	2h 24m 49s

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