I was also trying to install Google cloud sdk when I encountered this error. Here is what I did:
As @dannytech mentioned, I renamed the google-cloud-sdk.list so that it'll be ignored.
sudo mv /etc/apt/sources.list.d/google-cloud-sdk.list /etc/apt/sources.list.d/google-cloud-sdk.list1
Then I ran
sudo apt-get update && sudo apt-get install apt-transport-https
Then I replaced the original google-cloud-sdk.list back:
sudo mv /etc/apt/sources.list.d/google-cloud-sdk.list1 /etc/apt/sources.list.d/google-cloud-sdk.list
And then tried to install the Google cloud SDK again
sudo apt-get update && sudo apt-get install google-cloud-sdk
And it worked fine.
Also, @justin8 I created this workspace today but still apt-transport-https was not installed already. Hope you'll fix this.