Fix copy-paste error method-parameters.md

[andre1110]

When you assign new instance to the value type paramenter by reference, the changes are visible from the caller method

var instance = new TestStruct { Property = 0 };
AssignNewInstance(ref instance);
Console.WriteLine(instance.Property);
// 42

void AssignNewInstance(ref TestStruct local)
{
    local = new TestStruct { Property = 42 };
    return;
}
struct TestStruct
{
    public int Property { get; set; }
}

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