Increase test timeout (again) to fix s390x
    
    I'm honestly really impressed at this point with how slow s390x builders
    seem to get at this point. For context, it seems it's still possible to
    trigger test timeouts on s390x:
    
      4/274 lib: igt_conflicting_args               TIMEOUT 240.00 s
    
    This test is not even processing intensive, so I really have no idea why
    it takes so long but increasing the timeout forever seems to work.