bug#60340: 29.0.60; force-mode-line-update does not update tab line

[Juri Linkov]

> (defun random-name (_buffer &optional _buffers)
>   (format "tab %d" (random 1000)))
> (setq tab-line-tab-name-function #'random-name)
> (tab-line-mode)
>
> Then, eval:
>
> (force-mode-line-update)
>
> Every time that evals, I believe you should see the tab name update, but
> it does not. This makes it impossible to change tab names without
> changing buffer names as far as I can tell. There is likely something
> I'm missing, but per the docs, I believe force-mode-line-update should
> update tab lines. Passing `t' as ALL does not work either.

Does it help to override the cache key with something like this?

(defun tab-line-cache-key-default (_tabs)
  (list (random 1000)))