Prepare for upgrade to React 19

Co-authored-by: ayumi-signal <ayumi@signal.org>

ts/components/conversation/poll-message/PollVotesModal.dom.tsx

@@ -31,7 +31,7 @@ export function PollVotesModal({
   endPoll,
   canEndPoll,
   messageId,
-}: PollVotesModalProps): JSX.Element {
+}: PollVotesModalProps): React.JSX.Element {
   const maxVoteCount = useMemo(() => {
     return poll.votesByOption.values().reduce((max, voters) => {
       return Math.max(max, voters.length);