* [13030]: When a legacy gov proposal fails it's handler check, wrap the error in a ErrInvalidProposalContent (instead of ErrNoProposalHandlerExists).
* [13030]: Add changelog entry.
* [13030]: If the error is already a ErrNoProposalHandlerExists, just return it. Otherwise, wrap it as a ErrInvalidProposalContent.
Co-authored-by: Aleksandr Bezobchuk <alexanderbez@users.noreply.github.com>