tests: fix broken symlink
tests: fix broken symlink

`requirements2.5.txt` is pointing to `tests/requirements2.4.txt` while
it should point to `requirements2.4.txt` since they are in the same
directory.

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

ceph/ceph-ansible,font/ceph-ansible,fgal/ceph-ansible,ceph/ceph-ansible,font/ceph-ansible,fgal/ceph-ansible