Enable Ruff pytest-style (PT) rules

[fizyk]

Summary

Enable Ruff's pytest-style (PT) rule family in the project lint configuration and CI checks.

Rationale

The project does not currently enforce pytest-style rules. This means rules such as PT007, which requires a list for pytest.mark.parametrize values, are reported by external analysis but are not validated by the repository's configured lint checks.

Affected areas

• Ruff configuration
• Lint command or CI workflow that runs Ruff
• Existing test modules that violate enabled PT rules

Required changes

1. Enable the Ruff PT rule family in the project configuration.
2. Run the configured lint check against the repository.
3. Update existing tests or add explicit, documented rule exceptions where required.
4. Ensure CI fails when enabled PT rules are violated.

Acceptance criteria

• Ruff selects the PT rule family.
• The repository passes the configured Ruff lint command with the PT rule family enabled.
• CI enforces the same Ruff configuration.

Backlinks

• Pull request: Cleaner error message when the server is not installed - closes #1031 pytest-postgresql#1396
• Review comment: Cleaner error message when the server is not installed - closes #1031 pytest-postgresql#1396 (comment)

Requested by: @fizyk

---

Copied from dbfixtures/pytest-postgresql#1397