Currently with the GitHub connector it is only possible to connect to Metadata in GitHub.
You can find details of such an issue in the support ticket I created: 02231816 - GITHUB TABLES APPEARS ONLY RELATED TO METADATA
This is not very useful, instead it would be a great enhancement being able to extract data from tables located in a GitHub repository.
For instance, I am trying to access the following CSV file in order to import it in my app and use its data as a table.
https://github.com/owid/covid-19-data/tree/master/public/data/vaccinations/vaccionations.csv
This is not possible, currently the connector only permits to gather MetaData (such as repository names etc)