fix(rhum/v2.x): add key to code

Although this doesn't seem to be needed, some elements contain the same keys, so adding the key helps ensure DOM changes

src/components/markdown/CodeExtended.jsx

@@ -133,6 +133,7 @@ export default function CodeExtension({
   function renderSingleCodeBlock() {
     return (
       <code
+        key={children.toString()}
         className={getPrismJsClassNameForCodeBlock(className)}
       >
         {children}