you have not set your github username and password into your windows credentials. that's why this giving error.
add github credentials in your window
add your github account url, username and token password into your windows credentials.
1. go to window and search "credentials manager"
2. go to window credentials
3. click on "add a generic credential"
then perform this
NOTE: you can take
github url: git:https://github.com
username: -----------
password: ---------