Prepare for upgrade to React 19

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

ts/components/conversationList/SearchResultsLoadingFakeHeader.dom.tsx

@@ -5,6 +5,8 @@ import React from 'react';
 
 type PropsType = Record<string, never>;
 
-export function SearchResultsLoadingFakeHeader(_: PropsType): JSX.Element {
+export function SearchResultsLoadingFakeHeader(
+  _: PropsType
+): React.JSX.Element {
   return <div className="module-SearchResultsLoadingFakeHeader" />;
 }