What does the * behind the name of a game when creating a giveaway mean?

Bundle game?

The game was either in a bundle or it was exploited at some point or another. If you only give away games with a * then the max contrib value you can get is $30.

I indicates a game that's previously been in a bundle.

Bundle game's contributor value is calulated in a slightly different way than other games.

Additional info

It's considered a bundle/exploited game, and you will only get limited contributor value for gifting them. The value caps at $30 if you don't gift anything besides these games.