org-fast-tag-selection: Make group tags separator not break alignment

* lisp/org.el (org-fast-tag-selection): Start " : " group tags
separator before tag column in the menu.

Reported in https://orgmode.org/list/62f04f7c.d40a0220.9da67.0a2cSMTPIN_ADDED_BROKEN@mx.google.com

lisp/org.el

@@ -11755,7 +11755,9 @@ Returns the new tags string, or nil to not change the current settings."
 	      (while (equal (car tbl) '(:newline))
 		(insert "\n")
 		(setq tbl (cdr tbl)))))
-	   ((equal e '(:grouptags)) (insert " : "))
+	   ((equal e '(:grouptags))
+            (delete-char -3)
+            (insert " : "))
 	   (t
 	    (setq tg (copy-sequence (car e)) c2 nil)
 	    (if (cdr e)