Fix slider velocity changes not being undone correctly

Closes https://github.com/ppy/osu/issues/25239.

`LegacyEditorBeatmapPatcher.processHitObjectLocalData()` was already
supposed to be handling changes to hitobjects that will show up neither
when comparing the hitobjects themselves or the timing point with
"legacy" info stripped - so, in other words, changes to slider velocity
and samples.

However, a change to slider velocity requires default application to
take effect, so just resetting the value would visually fix the timeline
marker but not change the actual object. Calling
`EditorBeatmap.Update()` fixes this by way of triggering default
re-application.

This could probably be smarter (by only invoking the update when
strictly necessary, etc.) - but I'm not sure it's worth the hassle. This
is intended to be a quick fix, rather than a complete solution - the
complete solution would indeed likely entail a wholesale restructuring
of the editor's change handling.

osu.Game/Screens/Edit/LegacyEditorBeatmapPatcher.cs

@@ -123,6 +123,8 @@ namespace osu.Game.Screens.Edit
                     oldWithRepeats.NodeSamples.Clear();
                     oldWithRepeats.NodeSamples.AddRange(newWithRepeats.NodeSamples);
                 }
+
+                editorBeatmap.Update(oldObject);
             }
         }