You can’t really anonymously use a credit card. Privacy.com will let you give bogus info to the FOSS project if you really don’t trust the devs having your name, but you’ll have to give Privacy a bunch of info which is arguably an even bigger invasion of privacy. I suppose it’s a matter of who you trust.
Most donations will go through an intermediary like PayPal so it’s not like you’re giving them your credit card info directly.