header 'x-amz-security-token' with None

[gilcu2]

Hello, I see in your test test_task_4_build_auth_headers_for_the_request that when security_token==None you include a header 'x-amz-security-token' with None.
Is this necessary for something? I removed it manually because cause problems using the request with httpx and the call works.
If this is an error I can do a PR for fix it.
Thanks

[okigan]

I see, yea PR sounds good.