python: allow using allowed_errors.py (#7719)

See #7718. Fix it by renaming all `types.py` to `common_types.py`.

Additionally, add an advert for using `allowed_errors.py` to test any
added regex.

test_runner/regress/test_lsn_mapping.py

@@ -2,10 +2,10 @@ import re
 import time
 from datetime import datetime, timedelta, timezone
 
+from fixtures.common_types import Lsn
 from fixtures.log_helper import log
 from fixtures.neon_fixtures import NeonEnvBuilder, wait_for_last_flush_lsn
 from fixtures.pageserver.http import PageserverApiException
-from fixtures.types import Lsn
 from fixtures.utils import query_scalar