tests/posix/group_o_group: Fix copy pasta

Author: tavianator

tests/posix/group_o_group.sh

@@ -1,3 +1,3 @@
 # Regression test for
 # https://github.com/tavianator/bfs/issues/155
-bfs_diff basic -user 0 -o -user "$(id -g)"
+bfs_diff basic -group 0 -o -group "$(id -g)"