Consistent curve type check tests

[RickyDaMa]

Description

Relates to feedback on #4797

Use defcon APIs, not ufoLib2, since this is what Fontbakery expects

Add test

Note: using ufo.file_displayname caused an exception during tests as Ufo.file is not mocked

Fixed up the previous changelog entry as you changed the check ID in code, but not the changelog

Checklist

• [x] update CHANGELOG.md
• [x] wait for the tests to pass
• [ ] request a review