Add new webkitgtk build as workaround for file conflict issue
    
    The file conflict between older webkit2gtk4.1-jsc and new
    javascriptcoregtk4.1 is causing all Workstation update tests to
    fail on all Rawhide updates. This new version of webkitgtk adds
    obsoletes to javascriptcoregtk4.1 which we hope should fix it.
    Adding the x86_64 build directly as other arches aren't done
    yet, and we only run the Workstation update tests on x86_64
    anyway.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>