That's not what agnostic means. Most people who believe in God wouldn't say they can prove God exists, and they aren't agnostic.
Agnosticism is not about being uncertain, it's the position that the answer is unknowable or unknown - which is much stronger than merely being uncertain.
It would be better to ask, "Does a deity feature amongst your considerations when making a decision?"
I take it that's what people are mainly interested in anyway.
If this question was asked alongside the others in these questionnaires I think you'd see a high percentage of non-atheist responders agreeing.
Agnosticism has the greek root "gnosis", which means "knowledge". It's technically defined as a view that some things ("God" being a common, but not sole example) are unknowable. It's an epistemological concept.
Theism has the greek root "theos", meaning "God". Its primary concern is with the actual existence of God, so it's an ontological concept.
It's possible to think of agnosticism as side-stepping the theism debate by saying, "the nature of knowing matters more to me than the nature of being," but they're definitely compatible. You can say that the existence of God is unknowable (agnosticism,) but you believe that He's still out there (theism.)