rb_copy_generic_ivar correctly get the IV_HASH #10558

Job	Run time
Windows 2022/Visual C++ 2019 (check)	24m 30s
Windows 2025/Visual C++ 2019 (check)	27m 47s
Windows 11-arm/Visual C++ (btest test-basic test-tool)	17m 0s
Windows 2022/Visual C++ 2019 (test-bundled-gems)	21m 41s
Windows result	1s
	1h 30m 59s

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