Reenable test_gdb
    
    test_gdb now detects when the Python is optmized and gdb fails to
    read debug information:
    https://bugs.python.org/issue40019
    
    The following issues should now be fixed in Python 3.9.0 alpha 5
    
    * test_gdb skipped on s390x:
      https://bugzilla.redhat.com/show_bug.cgi?id=1678277
    * test_gdb skipped everywhere:
      https://bugzilla.redhat.com/show_bug.cgi?id=1734327
    
    Resolves: rhbz#1734327