test(sprite): destroy the working texture in the new sheet helper

CreateSheetOfSize built a Texture2D and never released it, while both sibling
helpers a few lines up destroy theirs after encoding. A Texture2D created in an
EditMode test is not collected on its own, so the helper leaked one per call
for as long as the run lasted.

The helper now matches the siblings exactly - same format arguments, same
Path.Combine style, same DestroyImmediate placement - which is the point: an
inconsistency between three functions doing the same job is what let this one
be written without the line.

Author: BurakErdemci

TestProjects/UnityMCPTests/Assets/Tests/EditMode/Tools/ManageSpriteTests.cs

@@ -104,16 +104,21 @@ private static string CreateNoiseSheet(string name, int side, bool assertOverCei
         /// <summary>A flat sheet of an exact pixel size, for grids that do not divide evenly.</summary>
         private static string CreateSheetOfSize(string name, int width, int height)
         {
-            var tex = new Texture2D(width, height);
-            var px = new Color32[width * height];
-            for (int i = 0; i < px.Length; i++) px[i] = new Color32(255, 0, 0, 255);
-            tex.SetPixels32(px);
+            var tex = new Texture2D(width, height, TextureFormat.RGBA32, false);
+            var pixels = new Color32[width * height];
+            for (int i = 0; i < pixels.Length; i++)
+                pixels[i] = new Color32(255, 0, 0, 255);
+            tex.SetPixels32(pixels);
             tex.Apply();
 
             string assetPath = $"{TempRoot}/{name}.png";
-            System.IO.File.WriteAllBytes(
-                System.IO.Path.Combine(Directory.GetParent(Application.dataPath).FullName, assetPath),
-                tex.EncodeToPNG());
+            string sysPath = Path.Combine(
+                Directory.GetParent(Application.dataPath).FullName, assetPath);
+            File.WriteAllBytes(sysPath, tex.EncodeToPNG());
+            // Both sibling helpers destroy their working texture here; this one did not, and
+            // a Texture2D built in an EditMode test is not collected on its own.
+            Object.DestroyImmediate(tex);
+
             AssetDatabase.ImportAsset(assetPath, ImportAssetOptions.ForceSynchronousImport);
             return assetPath;
         }