Corrected AddRange with single item

Author: Bart Koelman

test/JsonApiDotNetCoreTests/IntegrationTests/ResourceDefinitions/Reading/ResourceDefinitionReadTests.cs

@@ -331,7 +331,7 @@ public async Task Filter_from_resource_definition_is_applied_on_secondary_endpoi
         await _testContext.RunOnDatabaseAsync(async dbContext =>
         {
             await dbContext.ClearTableAsync<Planet>();
-            dbContext.Stars.AddRange(star);
+            dbContext.Stars.Add(star);
             await dbContext.SaveChangesAsync();
         });
 
@@ -387,7 +387,7 @@ public async Task Filter_from_resource_definition_is_applied_on_relationship_end
         await _testContext.RunOnDatabaseAsync(async dbContext =>
         {
             await dbContext.ClearTableAsync<Planet>();
-            dbContext.Stars.AddRange(star);
+            dbContext.Stars.Add(star);
             await dbContext.SaveChangesAsync();
         });