fix: missing prop key (#1291)

web/src/labs/marked/parser/Br.tsx

@@ -4,7 +4,7 @@ const renderer = (rawStr: string) => {
   const length = rawStr.split("\n").length - 1;
   const brList = [];
   for (let i = 0; i < length; i++) {
-    brList.push(<br />);
+    brList.push(<br key={i} />);
   }
   return <>{...brList}</>;
 };