How to catch any exception (System.Exception) without a warning in F#?

I tried to catch an Exception but the compiler gives warning: This type test or downcast will always hold

let testFail () =
    try
        printfn "Ready for failing..."
        failwith "Fails"
    with
    | :? System.ArgumentException -> ()
    | :? System.Exception -> ()

The question is: how to I do it without the warning? (I believe there must be a way to do this, otherwise there should be no warning)

Like C#

try
{
    Console.WriteLine("Ready for failing...");
    throw new Exception("Fails");
}
catch (Exception)
{
}