CI: Remove dlopen-test from valgrind blacklist
    
    Dlopen test was added to blacklist due to following reason:
    > Disable running dlopen-tests under Valgrind as their use of dlclose
    > makes Valgrind drop symbols and produce meaningless backtraces, which
    > cannot be matched with specific suppressions.
    
    It's true that dlclose makes meaningless backtraces but backtraces should
    not be generated otherwise there is a bug in some library which need to be
    fixed and not suppressed.
    
    Reviewed-by: Nikolai Kondrashov <Nikolai.Kondrashov@redhat.com>