If you’re trying to demonstrate real world programming skills then selecting and using an appropriate library is the best move (unless this is an unlikely case where there is some really compelling reason why a custom implementation would be preferable).

But if you want to make your own hash table for funsies or for educational purposes or whatever, you could add a note or comment stating that, if you’re concerned that prospective employers might get the impression that you will write everything from scratch even when it’s a bad idea.