use var_os in a few places

[xtqqczze]

Use var_os for LC_ALL, LC_TIME, etc.

Contributes to #11076

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!
Congrats! The gnu test tests/tail/pipe-f is now passing!

[cakebaker]

Thanks!