fix: error message in link_dependencies collision

[TyberiusPrime]

Just another case where we can exactly pinpoint the two causing pkgs.

Previous error message

FileExistsError: [Errno 17] File exists: '/nix/store/jyzfv9z981s6x1kqrf2k4k9hh0l5na38-cfxdb-23.12.1/LICENSE' -> '/nix/store/b2ayknndk4w7hhydibf32z7vi6y2r57p-test-venv/LICENSE'

new

FileExistsError: Trying to link /nix/store/jyzfv9z981s6x1kqrf2k4k9hh0l5na38-cfxdb-23.12.1/LICENSE to /nix/store/4k7px3i153anj7h46fiw29qanvrz7iny-test-venv/LICENSE, but that already exists. It links to /nix/store/nlkfllagsi9x98agw7rlxgvh5l3h11jx-crossbar-22.6.1/LICENSE.

[adisbladis]

I find the phrasing a little odd. Maybe change it to something like

FileExistsError(f"Linking path {target_path} to {path} failed. Existing target is a {"symlink" if target_path.is_symlink() else "regular file"}")

[TyberiusPrime]

The important part is that it tells you what the symlink is pointing to.
Maybe like this:

except FileExistsError:
                    msg = f"Linking path {target_path} to {path} failed because it already existed."
                    if Path(target_path).is_symlink():
                        msg += f" It is a symlink resolving to {Path(target_path).resolve()}."
                    raise FileExistsError(msg)