join: use show_error instead of eprintln

[cakebaker]

No description provided.

[oech3]

Is it able to add tests corresponging with 2>/dev/full SIGABRT caused by eprintln!().

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!