stderr was only produced when there was a real failure as it had been a
bit noisy previously, but has hidden actual problems. Now that there is
less noise, just output stderr all the time.
All changes in this patch were performed automatically with `shfmt` with
configuration flags specified in `.pre-commit-config.yaml`.
In addition to fixing whitespace the roundtrip through shfmt's AST also
transforms command substitutions
`cmd`
# becomes
$(cmd)
and some redirects
>&2 echo "msg"
# becomes
echo >&2 "msg"
