List<T>.Contains not showing overload

public void ContainedInList(IEnumerable<T> list, T value, IEqualityComparer<T> comparer)
{
    foreach(T element in list)
    {
        if (comparer.Equals(element, value))
            return true;
    }
    return false;
}

namespace System.Runtime.CompilerServices
{
    public class ExtensionAttribute : Attribute
    {
    }
}

public static class MyExtensions
{
    public static Contains<T>(this IEnumerable<T> list,
        T item, IEqualityComparer<T> comparer)
    {
        foreach (var i in list) if (comparer.Equals(item, i)) return true;
        return false;
    }
}