.NET 9 forward compatibility changes (#33421)

This doesn't switch the projects over to .NET 9, but it does make them work on .NET 9 when we decide to switch in the future.

Content.Server/NPC/Pathfinding/PathfindingSystem.Breadth.cs

@@ -11,8 +11,8 @@ public sealed partial class PathfindingSystem
     /// </summary>
     public record struct BreadthPathArgs()
     {
-        public Vector2i Start;
-        public List<Vector2i> Ends;
+        public required Vector2i Start;
+        public required List<Vector2i> Ends;
 
         public bool Diagonals = false;