fix(git): For git cli, tell users what config we aren't forwarding on error (#17477)

### What does this PR try to resolve?

With libgit2, we pass it Cargo's network settings. For git cli, we
don't, relying on git config.

For current git cli users,
they are largely using it to get the git config settings and could
negatively impact them if we forward settings.

For libgit2 users transitioning to git cli,
they likely also have git config settings already set.

To walk the line between these users,
we're just giving users transition to git cli a heads up on how to
resolve these problems.

Since we expect few people impacted and this to be short lived, we
aren't investing too much into the quality of the message, like checking
git config settings, or providing other dynamic details.

### How to test and review this PR?

I didn't add any tests for this, assuming the transition (#17329) will
have tests that cover this