724 fix incorrect redundant-expr error for isinstance on constra… #1723

Job	Run time
Test mypyc suite with 32-bit Python	7m 17s
Test suite with py38-ubuntu, mypyc-compiled	1m 31s
Test suite with py38-windows-64	30m 4s
Test suite with py39-ubuntu	27m 43s
Test suite with py310-ubuntu	27m 18s
Test suite with py311-ubuntu, mypyc-compiled	1m 7s
Test suite with py312-ubuntu, mypyc-compiled	1m 13s
mypyc runtime tests with py39-macos	4m 19s
mypyc runtime tests with py38-debug-build-ubuntu	4m 27s
Type check our own code (py38-ubuntu)	1m 39s
Type check our own code (py38-windows-64)	2m 1s
Formatting and code style with Black + ruff	35s
	1h 49m 14s

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