do not put objs-* in sandbox. Fix #5300

[cmsdmwmbot]

Jenkins results:

• Python3 Pylint check: failed
  • 1 warnings and errors that must be fixed
  • 30 comments to review
• Pycodestyle check: succeeded
  • 21 comments to review

Details at https://cmssdt.cern.ch/dmwm-jenkins/view/All/job/DMWM-CRABClient-PR-test/1054/artifact/artifacts/PullRequestReport.html

[belforte]

tested in https://github.com/dmwm/CRABServer/issues/8318