tangle: Fix :version keyword of org-babel-tangle-default-file-mode

* lisp/ob-tangle.el (org-babel-tangle-default-file-mode): Prefer
":package-version" to ":version".

The :version keyword should correspond to the Emacs version.  Using
the Org version leads to an incorrect help message:

  This variable was introduced, or its default value was changed, in
  version 9.6 of Emacs.

Instead go through :package-version so that the displayed message is

  This variable was introduced, or its default value was changed, in
  version 9.6 of the Org package that is part of Emacs 29.1.

lisp/ob-tangle.el

@@ -145,7 +145,7 @@ result.  The default value is `org-remove-indentation'."
 The default value 356 correspands to the octal #o544, which is
 read-write permissions for the user, read-only for everyone else."
   :group 'org-babel
-  :version "9.6"
+  :package-version '(Org . "9.6")
   :type 'integer)
 
 (defun org-babel-find-file-noselect-refresh (file)