yes: dedup tee()

[oech3]

Reuse 1st tee in loop to detect non-pipe stdout. Remove } else.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)

[cakebaker]

Thanks!