[PEP 695] Fix multiple nested classes don't work #13238

Job	Run time
Test mypyc suite with 32-bit Python	6m 45s
Test suite with Python nightly	13m 49s
Test suite with py38-ubuntu, mypyc-compiled	1m 24s
Test suite with py38-windows-64	12m 32s
Test suite with py39-ubuntu	12m 41s
Test suite with py310-ubuntu	13m 10s
Test suite with py311-ubuntu, mypyc-compiled	1m 0s
Test suite with py312-ubuntu, mypyc-compiled	1m 3s
mypyc runtime tests with py39-macos	4m 32s
mypyc runtime tests with py38-debug-build-ubuntu	4m 25s
Type check our own code (py38-ubuntu)	1m 44s
Type check our own code (py38-windows-64)	2m 26s
Formatting and code style with Black + ruff	34s
	1h 16m 5s

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