Avoid getting inline tasks when using imenu

* lisp/org.el (org-imenu-get-tree): browse only true headlines.

lisp/org.el

@@ -20248,7 +20248,7 @@ Show the heading too, if it is currently invisible."
   (mapc (lambda (x) (move-marker x nil)) org-imenu-markers)
   (setq org-imenu-markers nil)
   (let* ((n org-imenu-depth)
-	 (re (concat "^" outline-regexp))
+	 (re (org-get-limited-outline-regexp))
 	 (subs (make-vector (1+ n) nil))
 	 (last-level 0)
 	 m level head)