Poor error message when vindex/cmd/sumdbverify encounters a git repository with unexpected owner

I was trying github.com/transparency-dev/incubator/vindex/cmd/sumdbverify@main --mod_root /host in a container, where /host was a read-only mount of a git checkout on the container host. In this setup, I had an ownership mismatch, and I got somewhat confusing error messaged from sumdbverify: failed to create zip file: create zip from version control system /host: could not find a recognized version control system at "/host".

When I ran git directly, e.g., (cd /host && git log) I got a better error message that explained the problem

fatal: detected dubious ownership in repository at '/host'
To add an exception for this directory, call:

        git config --global --add safe.directory /host

It would be nice if the sumdbverify error reporting mentioned unexpected ownership, rather than telling me that there's no git repository.

(And running the suggested git config command solved the problem, and made sumdbverify happy).

Start at the vindex/cmd/sumdbverify command and reproduce the failure against a read-only git checkout with an ownership mismatch. Trace how the git error becomes the reported “could not find a recognized version control system” message; done means unexpected ownership is reported clearly while other repository-detection errors remain understandable.