Stop using basic auth

[javierggt]

Basic auth is being deprecated and needs to be replaced by token-based authentication:
https://developer.github.com/changes/2020-02-14-deprecating-password-auth/

[javierggt]

Token-based authentication is enabled in the github module, so what is missing is to change the name of the environmental variable in all workflows. Right now we have:

        GIT_USERNAME: chandra-xray
        GIT_PASSWORD: 

and we should have

        GITHUB_API_TOKEN: