Fix `AddItem` extension method of `UnitOfWorkExtensions`.

framework/src/Volo.Abp.Uow/Volo/Abp/Uow/UnitOfWorkExtensions.cs

@@ -19,14 +19,7 @@ public static class UnitOfWorkExtensions
     {
         Check.NotNull(unitOfWork, nameof(unitOfWork));
 
-        if (!unitOfWork.Items.ContainsKey(key))
-        {
-            unitOfWork.Items[key] = value;
-        }
-        else
-        {
-            unitOfWork.Items.Add(key, value);
-        }
+        unitOfWork.Items[key] = value;
     }
 
     public static TValue GetItemOrDefault<TValue>([NotNull] this IUnitOfWork unitOfWork, string key)

framework/test/Volo.Abp.Uow.Tests/Volo/Abp/Uow/UnitOfWorkExtensions_Tests.cs

@@ -21,6 +21,11 @@ public class UnitOfWorkExtensions_Tests : AbpIntegratedTest<AbpUnitOfWorkModule>
 
         uow.Items.ShouldContainKey("testKey");
         uow.Items.ContainsValue("testValue");
+
+        uow.AddItem("testKey", "testValue2");
+
+        uow.Items.ShouldContainKey("testKey");
+        uow.Items.ContainsValue("testValue2");
     }
 
     [Fact]