message: fix {{execute}} regex for multiline executables in QuickStart
diff: @@ -11,7 +11,7 @@ const useMultilineExecuteCommandShowdownExtension = () => {
  return useMemo(
  () => ({
  type: 'lang',
  - regex: /```[\n]((.*?\n)+)```{{execute}}/g,
  + regex: /```[\n]\s*((((?!```).)*?\n)+)\s*```{{execute}}/g,
  replace: (
  text: string,
  group: string,
  