Set --project-dir as working directory.

dbt creates `dbt_packages` in the working directory rather than in `--project-dir`.
This ensure that it creates it in the right place.

elementary/clients/dbt/dbt_runner.py

@@ -90,6 +90,7 @@ def _run_command(
                 check=self.raise_on_failure,
                 capture_output=(capture_output or quiet),
                 env=self._get_command_env(),
+                cwd=self.project_dir,
             )
         except subprocess.CalledProcessError as err:
             logs = list(parse_dbt_output(err.output.decode())) if err.output else []