bug#64686: 30.0.50; Tar mode @PaxHeader bug

[Eli Zaretskii]

> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Fri, 28 Jul 2023 13:47:39 +0200
> Cc: Eli Zaretskii <eliz@gnu.org>,
>  Devon Sean McCullough <emacs-hacker2017@jovi.net>,
>  64686@debbugs.gnu.org,
>  Stefan Monnier <monnier@iro.umontreal.ca>
> 
> maybe we should return a fresh vector each time instead of reusing a single 
> global object.

I had that in the prototype, but decided I didn't like too much
consing this would produce.