Update plurals in editor rotate button tooltip

Co-authored-by: Joseph Madamba <madamba.joehu@outlook.com>

osu.Game.Rulesets.Osu/Edit/PreciseRotationPopover.cs

@@ -70,7 +70,7 @@ private void load()
             };
             selectionCentreButton.Selected.DisabledChanged += isDisabled =>
             {
-                selectionCentreButton.TooltipText = isDisabled ? "Select more than one objects to perform selection-based rotation." : string.Empty;
+                selectionCentreButton.TooltipText = isDisabled ? "Select more than one object to perform selection-based rotation." : string.Empty;
             };
         }