I am sending out invitations to all Sage contributors with known GitHub accounts to join the sagemath organization (unless they are already a Member).
If you accept the invitation, your contributions to Sage (tickets, comments, ...) will be connected to your GitHub account.
Otherwise, we have to create a placeholder account ("mannequin") for your contribution. Our GitHub migration team contact has assured us that it will be possible to link mannequins to real accounts later; but it is an extra step, so it pays off to respond quickly to the invitation.