Repository comparison fail when default branches have no common ancestor

[Jackenmen]

I get this error for one of the forks I have:

Error gathering the repository list: failed to compare repository with upstream: jack1142/compose: GET https://api.github.com/repos/docker/compose/compare/v2...jack1142:master: 404 No common ancestor between v2 and jack1142:master. [].

It appears that this fork has been created when a different branch was the default branch and the branch that is now the default branch is completely new (created without a base, e.g. with --orphan).

[osama-raddad]

same problem here

[caarlos0]

happy to review a pr for this

[github-actions]

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