pkgrepo state: add missing import of `sys` module

************* Module salt.states.pkgrepo
salt/states/pkgrepo.py:303: [E0602(undefined-variable), managed] Undefined variable 'sys'
salt/states/pkgrepo.py:379: [E0602(undefined-variable), absent] Undefined variable 'sys'
Merge pull request #11060 from cvrebert/patch-1

pkgrepo state: add missing import of `sys` module