specs: undo chdir in before black by returning to $CWD in after.
specs: undo chdir in before black by returning to $CWD in after.

* specs/posix_glob_spec.yaml (specify posix.glob): Get current
working directory in before block, and chdir back to it in after
black.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

luaposix/luaposix