Fix swells not being correctly treated in editor gameplay test

Closes https://github.com/ppy/osu/issues/28989.

Because swell ticks are judged manually by their parenting objects,
swell ticks were not given a start time (with the thinking that there
isn't really one *to* give). This tripped up the "judge past objects"
logic in `EditorPlayer`, since it would enumerate all objects
(regardless of nesting) that are prior to current time and mark them as
judged. With all swell ticks having the default start time of 0 they
would get judged more often than not, leading to behaviour weirdness.

To resolve, give swell ticks a *relatively* sane start time equal to
the start time of the swell itself.

osu.Game.Rulesets.Taiko/Objects/Swell.cs

@@ -33,6 +33,7 @@ namespace osu.Game.Rulesets.Taiko.Objects
                 cancellationToken.ThrowIfCancellationRequested();
                 AddNested(new SwellTick
                 {
+                    StartTime = StartTime,
                     Samples = Samples
                 });
             }