tests: activitypub: fix broken test due to invalid child object

test/web/activity_pub/activity_pub_test.exs

@@ -93,7 +93,11 @@ test "removes doubled 'to' recipients" do
           to: ["user1", "user1", "user2"],
           actor: user,
           context: "",
-          object: %{}
+          object: %{
+            "to" => ["user1", "user1", "user2"],
+            "type" => "Note",
+            "content" => "testing"
+          }
         })
 
       assert activity.data["to"] == ["user1", "user2"]