fix asset load conflict always showing multiple-mod form

docs/release-notes.md

@@ -9,6 +9,7 @@
   * Improved [command-line arguments](technical/smapi.md#command-line-arguments) on Linux/macOS:
     * Added `--use-current-shell` to avoid opening a separate terminal window.
     * Fixed `--no-terminal` still opening a terminal window, even if nothing is logged to it (thanks to Ryhon0!).
+  * Fixed warning text when a mod causes an asset load conflict with itself.
 
 * For mod authors:
   * Added [content events](https://stardewvalleywiki.com/Modding:Modder_Guide/APIs/Events#Content), which will replace `IAssetEditor` and `IAssetLoader` in SMAPI 4.0.0. These include new features not supported by the old API like content pack labels.

src/SMAPI/Framework/ContentManagers/GameContentManager.cs

@@ -400,7 +400,10 @@ namespace StardewModdingAPI.Framework.ContentManagers
                 return true;
             }
 
-            string[] loaderNames = loaders.Select(p => p.Mod.DisplayName).ToArray();
+            string[] loaderNames = loaders
+                .Select(p => p.Mod.DisplayName)
+                .Distinct()
+                .ToArray();
             string errorPhrase = loaderNames.Length > 1
                 ? $"Multiple mods want to provide '{info.Name}' asset ({string.Join(", ", loaderNames)})"
                 : $"The '{loaderNames[0]}' mod wants to provide the '{info.Name}' asset multiple times";