CI: Do not use valgrind for dummy-child
    
    There was a bug in valgrind < 3.13 which override some log files
    and therefore there was missing errors for shell wrappers generated
    by libtool for dummy-child.
    
    https://bugs.kde.org/show_bug.cgi?id=162848
    
    We could add more suppressions for errors/leaks in bash to our suppression
    file but dummy child is built just for test purposes. Another possible solution
    would to avoid linking dummy-child with internal libraries; So libtool
    would not generate shell wrapper for dummy-child.
    But the simplest think is to ignore all errors for dummy-child.
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
    (cherry picked from commit 223f4ff3cd9136414a8b593587f5742bf2c914cd)
    (cherry picked from commit 365ab04d84ff12843f6bd94d03d3d5a224e5bf4c)