runner: 'static final' to declare constants when it isn't an interface

Change-Id: Iea1e672e5468b66fd1ba5389bd781f03d0c7f419
Reviewed-on: https://gerrit.libreoffice.org/11931
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>