Add missing the TOML section header [tool.render-engine.cli] #26

The test configuration at lines 84-88 is missing the TOML section header [tool.render-engine.cli], so the config values will not be read correctly. The test expects module, site, and editor to be None because _config_loaded=True is passed, but this makes the test intention unclear. Consider adding the section header for completeness and clarity about what is being tested.

Originally posted by @Copilot in #22 (comment)