Many atheists uphold scepticism as a virtue, believing that scepticism inherently leads to atheism, or that atheism is by nature a more sceptical position. But we must remember that scepticism, per se, is always scepticism of something.
Atheists are sceptical of theism.
Theists are sceptical of atheism.
It is agnostics who are truly sceptical, as will challenge anyone’s positive claims on the matter at all.