fix test errors in core_external\external_api_test

[usqfowlerj]

Checklist

• [x] the contributor license agreement is signed — I had signed it under a different github username (@jonof)
• [x] commit message follows commit guidelines
• [ ] screenshots are included showing significant UI changes — N/A
• [ ] documentation is changed or added — N/A

Description of change

Fix for issue #99 to use an appropriate value for the $required argument, as exposed by core_external\external_api_test::test_all_external_info.