t4129: fix setfacl-related permissions failure

t4129: fix setfacl-related permissions failure

When running this test in Cygwin, it's necessary to remove the inherited
access control lists from the Git working directory in order for later
permissions tests to work as expected.

As such, fix an error in the test script so that the ACLs are set for
the working directory, not a nonexistent subdirectory.

Signed-off-by: Adam Dinwoodie <adam@dinwoodie.org>
Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>