bug#41604: guix pull impossible after rebasing a local repository

[John Soo]

Hi Guix,

I use a local git repo with branch that I specify in channels.scm.
My usual workflow is:

1. rebase on origin
2. guix pull

This stopped working with the following error:

Updating channel 'guix' from Git repository at 
'file:///home/john/projects/guix/.git'...
guix pull: error: aborting update of channel 'guix' to commit 
1444040933ac35b967720288dc30ed70e5481ed3, which is not a descendant of 
57518fc7bf1efc899c0dabaa76685a319661f8e4
hint: This could indicate that the channel has been tampered with and is trying 
to
force a roll-back, preventing you from getting the latest updates.  If you think
this is not the case, explicitly allow non-forward updates.

After removing $HOME/.cache/guix I get the following error:
guix pull: error: Git error: object not found - no match for id 
(57518fc7bf1efc899c0dabaa76685a319661f8e4)

Many thanks,

John