Bump dependency on swh-scheduler 0.0.39

requirements-swh.txt

 swh.core >= 0.0.44
 swh.model >= 0.0.27
 swh.objstorage >= 0.0.17
-swh.scheduler >= 0.0.26
+swh.scheduler >= 0.0.39
 swh.storage >= 0.0.106