Make OpenSSL::Digest subclasses Ractor-safe #12897

Job	Run time
Windows 2025/Visual C++ 2022 (test-bundled-gems)	21m 15s
Windows 2022/Visual C++ 2022 (check)	12m 12s
Windows 11-arm/Visual C++ (btest test-basic test-tool)	18m 42s
Windows 2025/Visual C++ 2022 (check)	14m 40s
Windows result	2s
	1h 6m 51s

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