It's come up here in a few comments before.
Perhaps not 100% physically shared infra but there's references of architecture overlap such as "The GitHub-hosted runner application is a fork of the Azure Pipelines Agent."
https://docs.github.com/en/actions/concepts/runners/github-h...
https://github.com/actions/runner-images#about
A few threads where blips have affected both services.
https://news.ycombinator.com/item?id=42781922