fix(markdown): don't remove char before `#` (#23151)

lib/util/markdown.ts

@@ -6,7 +6,7 @@ import { regEx } from './regex';
 export function sanitizeMarkdown(markdown: string): string {
   let res = markdown;
   // Put a zero width space after every # followed by a digit
-  res = res.replace(regEx(/\W#(\d)/gi), '#​$1');
+  res = res.replace(regEx(/(\W)#(\d)/gi), '$1#​$2');
   // Put a zero width space after every @ symbol to prevent unintended hyperlinking
   res = res.replace(regEx(/@/g), '@​');
   res = res.replace(regEx(/(`\[?@)​/g), '$1');