[fix] throw error when using enhance on GET forms

[dummdidumm]

closes #7896
closes #7972

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[Conduitry]

I agree with not including the helpful error message in prod builds - but I was wondering whether we might want to do something here in that case, even if it means just returning early so that the action is a no-op? Completely skipping the check is probably fine if that's what other people want to do, but I wanted to at least bring it up.

[dummdidumm]

I'm not sure the extra bytes are worth it - if this made it to production, the noop won't help much, especially if you maybe want this to run with JS only anyway.