Add missing workdir parameter when calling OAR's API

OAR's API use the workdir parameter to define where to put the
oarapi.subscript file.
3 jobs for bugs/#12478 in 22 minutes (queued for 3 seconds)
Status Job ID Name Coverage
  Lint
passed #858638
grid5000-docker
rubocop

00:01:33

 
  Test
passed #858639
grid5000-docker
test-for-buster

00:09:59

87.44%
 
  Deb
passed #858640
grid5000-docker
deb-for-buster

00:10:27