Describe the bug
When using renku login to access a private repository, every git pull or push operation prints an error message while the operation succeeds. We should find the source of this message and eliminate it.

To Reproduce

1. Clone a private project using it's http address
2. renku login <remote>
3. git pull

bad input: xpc2FmYWVlQGVwZmwuY2giLCJnaXZlbl9uYW1lIjoiTW9oYW1tYWQiLCJmYW1pbHlfbmFtZSI6IkFsaXNhZmFlZSIsImVtYWlsIjoibW9oYW1tYWQuYWxpc2FmYWVlQGVwZmwuY2gifQ.odMIi4hBPSUciu0imeFHwy-QhaMfiGwe8HN9P1jHK_2AESqs85CRfSg87ZSun_XuVPvKxls-r2edJRDTqxiwr45mPjBMGIuteZFrwTcpwjKnozJppypIuEl0_zyLxevseqrDi8ybCmHP3EEwxMcHFcA3O-aouZ3avjRLvFLs5q5MHCMyZc7x1N-TgGSNuI55cCshMVJ-3Yrzi4GUH5MU6HmA0pd3vMGo_WO6ppuLI8iqcVZ_BnFoMJ9wd-RhSjXk6XAsocBrA6eNxq7QweD2q3Pr1gDlsY6FOc00W4Zpx58jUYKYsAfEnlnY2joWLDPsBkPS3_-YYPVrdRm7CCEuTQ
Already up to date.

Additional context
We use git credentials helper to pass the KC access token to git (using the renku credentials command). The printed message is part of this access token.

Alternative
We should try to use the ssh keys when doing renku login instead of the access token and git credentials helper. Look into this option first before spending time on the bug.