It's theoretically helpful to at least put in a no-warranties clause. But sqlite as maybe the most popular public domain project worldwide doesn't (instead having just the declaration and a blessing). I mostly settled on the Unlicense https://unlicense.org/ over just declaring 'public domain' or 'CC0' as a simple text blob to paste in, and in the event of a significant contribution from someone else, there's a simple text blurb to ask them to say 'yes' to in order to keep the code unencumbered.