recent org-export-copy-buffer incompatible with Emacs < 28

[Kyle Meyer]

Hi Ihor,

b45911d41 (org-export-copy-buffer: Prevent saving to disk, 2022-10-07)
uses `always', but that function isn't available until Emacs 28.1,
specifically 825aed11d26 (Add the `always' function, 2021-02-20).