Fix orleans grain->persistence->index page

[ShaoHans]

Summary

On the page https://learn.microsoft.com/en-us/dotnet/orleans/grains/grain-persistence/?pivots=orleans-7-0 , the code snippet DateOfBirth property missing { get; set; }

[Serializable]
public class ProfileState
{
    public string Name { get; set; }

    public Date DateOfBirth
}

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Internal previews

📄 File	🔗 Preview link
docs/orleans/grains/grain-persistence/index.md	Grain persistence