Short answer
No, it's not safe, but the risk is low if it was just a lick. The mandarin itself is only a mild concern, but the sugar and other additives in gummy vitamins can upset a cat's stomach. Watch your cat for vomiting, diarrhea, or loss of appetite over the next day. If you see any of those signs, contact your regular veterinarian.
Mandarin — Food safety facts
Feed with care · Cats · full breakdown on the linked food page
A small segment of flesh is usually tolerated; peel and seeds are not.
The full verdict, portion guidance and serving notes are collected on the Mandarin food facts page.