I was trying to push my repository from GitLab local server to GitHub.com and encountered this error.
Can anyone tell me how to fix this? Thanks.
PS. I’m trying to push a repository from local server to GitHub because I’m trying to check if they would actually connect. 
Is your local GitLab server host permitted access to the internet? The failure suggests that it is unable to resolve a public domain address (of github.com), indicating lack of an internet gateway and/or upstream DNS resolver configuration.
You can log into the self-managed GitLab host(s) and check if the internet connectivity is setup properly:
nslookup github.com
traceroute github.com
curl -v https://github.com