Due to our HTTP client default behavior, an `Accept` header is added to
all API requests. This is fine for all commands except `gh api`, where
the user should ideally have fine-grained control over most aspects of
HTTP requests and where there should be little to no defaults in general.
This ensures that while having git remotes to point to either
`github.com` or authenticated GHE instances, adding another git remote
pointing to an unrelated host won't change the remote resolution in any
way, even if the unrelated remote is called `upstream` or `github` (and
thus normally took precedence).
