if the .key file has ExpiredAt and expired, it will always generate new .key file

[liugt34]

in FileSystemStore.cs this code always return the first file, so it will generate new file repeatly.

private string GetCurrentFile()
{
    var files = Directory.GetFiles(KeysPath.FullName, $"*current*.key");
    if (files.Any())
        return Path.Combine(KeysPath.FullName, files.First());

    return Path.Combine(KeysPath.FullName, $"{_options.Value.KeyPrefix}current.key");
}