Error when timescaledb not installed in source database

[JamesGuthrie]

When run against a database without timescaledb:

> timescale-doctor postgres://postgres:1@localhost:5432
Traceback (most recent call last):
  File "/home/james/workspace/doctor/venv/bin/timescale-doctor", line 8, in <module>
    sys.exit(main())
  File "/home/james/workspace/doctor/venv/lib/python3.10/site-packages/doctor/cli.py", line 57, in main
    check_rules(dsn)
  File "/home/james/workspace/doctor/venv/lib/python3.10/site-packages/doctor/__init__.py", line 83, in check_rules
    for report in rule.execute(conn, rule.message):
  File "/home/james/workspace/doctor/venv/lib/python3.10/site-packages/doctor/__init__.py", line 62, in execute
    cursor.execute(self.query) # pylint: disable=E1101
  File "/nix/store/khvw06lqds60i0npy58zs27xpwb8x0d9-python3.10-psycopg2-2.9.5/lib/python3.10/site-packages/psycopg2/extras.py", line 236, in execute
    return super().execute(query, vars)
psycopg2.errors.UndefinedTable: relation "_timescaledb_catalog.hypertable" does not exist
LINE 5:       FROM _timescaledb_catalog.hypertable ht
                   ^