Fix --admin bug

[vpchung]

Fixes #246

Changelog

• add additional check in _validate_admin_permissions() that checks whether project is already publicly accessible
• formatting

Preview

Before

$ challengeutils validate-project 9731653 syn28590455 --admin "RARE-X Organizers"
INFO:challengeutils.__main__:{'submission_errors': 'Project is private; please update its sharing settings. Writeup should be shared with RARE-X Organizers.', 'submission_status': 'INVALID'}

After

$ challengeutils validate-project 9731653 syn28590455 --admin "RARE-X Organizers"
INFO:challengeutils.__main__:{'submission_errors': '', 'submission_status': 'VALIDATED'}