using ScrollType::Drag looks the safest choice

rather than DontKnow, Drag assumptions seem to fit best

Change-Id: Iae92b29d33e69410c67b43fabb933018f1277abf
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/137809
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/vcl/unx/gtk3/gtkinst.cxx b/vcl/unx/gtk3/gtkinst.cxx
index 06c9d70..158bc84 100644
--- a/vcl/unx/gtk3/gtkinst.cxx
+++ b/vcl/unx/gtk3/gtkinst.cxx
@@ -8557,7 +8557,7 @@ public:

    virtual ScrollType get_scroll_type() const override
    {
        return ScrollType::DontKnow;
        return ScrollType::Drag;
    }

    virtual ~GtkInstanceScrollbar() override