fix typo: dupe.testcase not dupe.testcases
    
    Summary: This broke result reporting if any dupes were present.
    
    Test Plan: Try reporting some results with dupes.
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D477