Update Windows version boundary for Composite ML-DSA

[PranavSenthilnathan]

#129612 hardcodes a Windows version as the boundary where Composite ML-DSA was introduced. This currently references a preview version of Windows, but it should reference the next non-preview release. Once Windows has an official release with Composite ML-DSA, update the version.

Note: if Composite ML-DSA support is backported to older Windows versions, then it will need to be updated again to those new, lower versions. The tests that will likely fail are:

System.Security.Cryptography.Tests.CompositeMLDsaFactoryTests.IsSupported_AgreesWithPlatform
System.Security.Cryptography.Tests.CompositeMLDsaFactoryTests.IsAlgorithmSupported_AgreesWithPlatform

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