fix: network scene manager UNITY_INCLUDE_TESTS (#1265)

Converting all references of #if UNITY_EDITOR || DEVELOPMENT_BUILD over to #if UNITY_INCLUDE_TESTS

Remove a check that no longer is pertinent and had a terrible comment that didn't explain what the check was for or why we didn't create and register the DDOL scene like we normally would.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/SceneManagement/NetworkSceneManager.cs

@@ -99,7 +99,7 @@ public class NetworkSceneManager : IDisposable
 
         // TODO: Remove `m_IsRunningUnitTest` entirely after we switch to multi-process testing
         // In MultiInstance tests, we cannot allow clients to load additional scenes as they're sharing the same scene space / Unity instance.
-#if UNITY_EDITOR || DEVELOPMENT_BUILD
+#if UNITY_INCLUDE_TESTS
         private readonly bool m_IsRunningUnitTest = SceneManager.GetActiveScene().name.StartsWith("InitTestScene");
 #endif
 
@@ -320,22 +320,10 @@ internal NetworkSceneManager(NetworkManager networkManager)
             {
                 DontDestroyOnLoadScene = networkManager.gameObject.scene;
             }
-            else // Otherwise, we have to create a GameObject and move it into the DDOL to get the scene
+            else
             {
-
-#if UNITY_EDITOR || DEVELOPMENT_BUILD
-                // During unit and integration tests, we could initialize and then enable scene management
-                // which would make this generate an extra GameObject per instance. The DontDestroyOnLoadScene
-                // is internal so tests that are using multiInstance and that are moving NetworkObjects into
-                // the DDOL scene will have to manually set this. Otherwise, we can exclude DDOL stuff completely
-                // during unit testing.
-                if (m_IsRunningUnitTest)
-                {
-                    return;
-                }
-#endif
-                // Create our DDOL GameObject and move it into the DDOL scene so we can register the DDOL with
-                // the NetworkSceneManager and then destroy the DDOL GameObject
+                // Otherwise, we have to create a GameObject and move it into the DDOL in order to
+                // register the DDOL scene handle with NetworkSceneManager
                 var myDDOLObject = new GameObject("DDOL-NWSM");
                 UnityEngine.Object.DontDestroyOnLoad(myDDOLObject);
                 DontDestroyOnLoadScene = myDDOLObject.scene;
@@ -799,7 +787,6 @@ private void OnClientUnloadScene(uint sceneEventId)
                 ClientId = m_NetworkManager.LocalClientId   // Server sent this message to the client, but client is executing it
             });
 
-
 #if UNITY_INCLUDE_TESTS
             if (m_IsRunningUnitTest)
             {
@@ -973,7 +960,7 @@ private void OnClientSceneLoadingEvent(uint sceneEventId)
                 return;
             }
 
-#if UNITY_EDITOR || DEVELOPMENT_BUILD
+#if UNITY_INCLUDE_TESTS
             if (m_IsRunningUnitTest)
             {
                 // Send the loading message