Prevent policy from being supplied with the wrong actions

[WhatisRT]

Those governance actions that cannot cause a script to run on proposal should prevent that proposal from being supplied. There should be a check next to ∙ (∃[ u ] a ≡ ChangePParams u ⊎ ∃[ w ] a ≡ TreasuryWdrl w → p ≡ ppolicy) in GOV where in the negation of that case, we check p ≡ nothing.