It looks like there was a fix pushed 11 hours ago to resolve this same error message, and this may be related to your issue. https://github.com/actions/virtual-environments/issues/675
https://github.com/ebiggers/fscryptctl/commit/527405ff76671383c38ad58fbdff4dfa5e03c7fe
Please try running sudo apt-get update again.
Also, make sure to check your NSG rules and make sure that it is allowing outbound traffic on port 80.
Related discussion.