CarthageServerRole fails when run from an installed carthage-runner

`copy_in_carthage` setup task calls `rsync_git_tree` on `os.path.dirname(carthage.__file__)` which fails with
```
sh.ErrorReturnCode_128:

RAN: /usr/bin/git rev-parse --show-toplevel

STDOUT:

STDERR:
fatal: not a git repository (or any of the parent directories): .git
```

Start with the copy_in_carthage setup task and trace its call to rsync_git_tree using os.path.dirname(carthage.__file__). Reproduce the failure with an installed carthage-runner, then verify that the task completes without requiring the installed package directory to be a Git repository.

Written by the indexing model from the issue text.