patch 9.1.2137: test: Update tests for OpenBSD

patch 9.1.2137: test: Update tests for OpenBSD

Problem:  Some tests are not valid on OpenBSD.
Solution: Add CheckNotOpenBSD, use it to skip certain tests
          (Kevin Goodsell).

Test_readdirex_sort performs locale-dependent sorting. OpenBSD has
minimal locale support.

Test_stdin_no_newline hangs on OpenBSD and FreeBSD. I don't know exactly
why, but it may be due to bash not exiting at the end of the test. This
is skipped in the FreeBSD CI runs because bash is not installed.

Test_detect_fifo uses /dev/fd/ files (via process substitution) as
FIFOs. On OpenBSD the files in /dev/fd are not FIFOs.

closes: #19351

Signed-off-by: Kevin Goodsell <kevin-opensource@omegacrash.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>