ZTS: Fix 'could not unmount datasets' on Alma 9 (#15542)

Many tests are failing on AlmaLinux 9 because ZTS could not destroy the
pool in cleanup.  This was due to $PWD being set to '.' instead of the
expected full path.  This patch sets $PWD to the full path.

Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Don Brady <don.brady@delphix.com>

tests/zfs-tests/include/libtest.shlib

@@ -37,6 +37,12 @@
 
 . ${STF_SUITE}/include/tunables.cfg
 
+# On AlmaLinux 9 we will see $PWD = '.' instead of the full path.  This causes
+# some tests to fail.  Fix it up here.
+if [ "$PWD" = "." ] ; then
+	PWD="$(readlink -f $PWD)"
+fi
+
 #
 # Apply constrained path when available.  This is required since the
 # PATH may have been modified by sudo's secure_path behavior.