Add MarkNonNullableReferenceTypesAsRequired to DeepCopy

Without this change the setting will not be set when getting
SchemaGeneratorOptions from DI in SchemaGenerator

src/Swashbuckle.AspNetCore.SwaggerGen/DependencyInjection/ConfigureSchemaGeneratorOptions.cs

@@ -41,6 +41,7 @@ private void DeepCopy(SchemaGeneratorOptions source, SchemaGeneratorOptions targ
             target.DiscriminatorValueSelector = source.DiscriminatorValueSelector;
             target.UseAllOfToExtendReferenceSchemas = source.UseAllOfToExtendReferenceSchemas;
             target.SupportNonNullableReferenceTypes = source.SupportNonNullableReferenceTypes;
+            target.MarkNonNullableReferenceTypesAsRequired = source.MarkNonNullableReferenceTypesAsRequired;
             target.SchemaFilters = new List<ISchemaFilter>(source.SchemaFilters);
         }
 
@@ -50,4 +51,4 @@ private TFilter CreateFilter<TFilter>(FilterDescriptor filterDescriptor)
                 .CreateInstance(_serviceProvider, filterDescriptor.Type, filterDescriptor.Arguments);
         }
     }
-}
+}