If it matters ethically, then asking the question already provides the answer because foregoing actions which might be gotten away with is what it means to act ethically.
If it matters legally pay your attorney for legal advice, because there is no government agency that enforces licenses, the degree to which a license matters is the degree to which someone is willing to lawyer up.
You're just punting on the question. To rephrase, does it matter ethically, legally, or at all?
(Yes, I understand that if you're basing a business off it then it matters legally differently than if you're just hacking away on a hobby project, but the law covers all things and ethics is not confined to hobbies.)
When you use the word 'it', are you referring to "giving credit", or the question "Do I need to give credit"?
The former would mean "If giving credit matters ethically, then asking the question provides the answer [which is yes.]". But that's just asking the same question as OP. Does giving credit matter?
The latter would mean "If you felt like you might need to give credit, that the answer to that question matters ethically, then that provides the answer [which is yes, you need to give credit]". But that sounds wrong to me. That kind of logic would turn every positive impulse into an instant obligation.
If it matters legally pay your attorney for legal advice, because there is no government agency that enforces licenses, the degree to which a license matters is the degree to which someone is willing to lawyer up.
If it doesn't matter, it doesn't matter.