Do not error out when fetching from second remote

In `git_remote_update_tips()`, it prepares `FETCH_HEAD` file. If `HEAD` 's remote is not the same as the fetching remote, it raised an error.

This pull request fixes the issue.
This would silence every single error from `rtransform()` including OOM. If what you're trying to do is skip this when the upstream remote is a different one, then write exactly that.