Route pgjsonb database errors through Salt's logger instead of stderr

[co-cy]

What does this PR do?

salt/returners/pgjsonb.py has eight error-handling sites in _get_serv, _purge_jobs and _archive_jobs that write psycopg2.DatabaseError messages directly to sys.stderr and re-raise. On a daemonized master sys.stderr ends up in systemd's journal at best (or /dev/null at worst) — never in the configured log_file / syslog destination. Operators that scrape Salt's log file have no idea those database errors happened.

This PR replaces every sys.stderr.write with log.exception(...) carrying a description of the operation that failed, so the message and a full traceback reach Salt's configured log destination. The dead error = err.args assignment is removed, the now-unused import sys is dropped, and raise err is normalised to bare raise to preserve the original traceback. Behaviour (rollback, re-raise) is unchanged — only the visibility of the error changes.

The asymmetric except Exception block on _archive_jobs jids-insert is updated to use log.exception for consistency, but it is left in place for the same scope reason — sorting that asymmetry out belongs in a separate PR.

What issues does this PR fix or reference?

Fixes #69048

Previous Behavior

except psycopg2.DatabaseError as err:
    error = err.args
    sys.stderr.write(str(error))
    cursor.execute("ROLLBACK")
    raise err

The error message went to stderr (journal / /dev/null) and never to the configured Salt log. The exception still propagated, but with a synthetic traceback (because of raise err instead of bare raise).

New Behavior

except psycopg2.DatabaseError:
    log.exception("pgjsonb: failed to purge salt_returns")
    cursor.execute("ROLLBACK")
    raise

The error message and the full traceback are routed through log.exception to Salt's configured logger. The original traceback is preserved.

Merge requirements satisfied?

• Docs (no user-facing change; not required)
• Changelog — changelog/69048.fixed.md
• Tests written/updated — see tests/pytests/unit/returners/test_pgjsonb.py:
  • test__purge_jobs_logs_via_salt_logger_and_reraises_on_db_error
  • test__archive_jobs_logs_via_salt_logger_and_reraises_on_db_error
  • test__get_serv_logs_via_salt_logger_and_reraises_on_yield_error

Commits signed with GPG?

No.