fix: PlayerSpawnObjectVisibilityTests test instability (#3547)

Adjusting the PlayerSpawnObjectVisibilityTests so that it provides some
additional time for the deferred NetworkShow message to be processed.

[MTT-12639](https://jira.unity3d.com/browse/MTT-12639)

## Changelog

NA

## Testing and Documentation

- Includes integration test adjustments.
- No documentation changes or additions were necessary.

## Backport
No up-port is needed as this appears to be specific to v1.x.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Tests/Runtime/NetworkObject/PlayerSpawnObjectVisibilityTests.cs

@@ -13,7 +13,6 @@ namespace Unity.Netcode.RuntimeTests
     internal class PlayerSpawnObjectVisibilityTests : NetcodeIntegrationTest
     {
         protected override int NumberOfClients => 0;
-
         public enum PlayerSpawnStages
         {
             OnNetworkSpawn,
@@ -63,6 +62,25 @@ protected override void OnCreatePlayerPrefab()
             base.OnCreatePlayerPrefab();
         }
 
+        /// <summary>
+        /// Bypassing this on v1.x as the deferred show message could be processed on the next
+        /// frame from when the client registers having connected.
+        /// </summary>
+        protected override bool ShouldWaitForNewClientToConnect(NetworkManager networkManager)
+        {
+            return false;
+        }
+
+        /// <summary>
+        /// Validate that the player object is spawned on the client side.
+        /// </summary>
+        /// <returns></returns>
+        private bool ClientSpawnedPlayer()
+        {
+            var playerObject = m_ClientNetworkManagers[0].LocalClient.PlayerObject;
+            return playerObject != null && playerObject.IsSpawned && playerObject.IsOwner;
+        }
+
         /// <summary>
         /// Tests the scenario where under a client-server network topology if a player prefab
         /// is spawned by the server with no observers but the player prefab itself has server
@@ -81,7 +99,17 @@ public IEnumerator NetworkShowOnSpawnTest([Values] PlayerSpawnStages spawnStage)
 
             yield return CreateAndStartNewClient();
 
-            yield return new WaitForSeconds(0.25f);
+            // Wait for the new client to connect
+            yield return WaitForClientsConnectedOrTimeOut();
+            AssertOnTimeout($"Timed out waiting for client to connect!");
+            OnNewClientStartedAndConnected(m_ClientNetworkManagers[0]);
+
+            // Wait for the new client to have spawned the player
+            yield return WaitForConditionOrTimeOut(ClientSpawnedPlayer);
+            AssertOnTimeout($"Timed out waiting for client to spawn its player object!");
+
+            // Provide some time to assure there are no additional attempts to spawn the same instance
+            yield return new WaitForSeconds(0.5f);
 
             NetcodeLogAssert.LogWasNotReceived(LogType.Warning, new Regex("but it is already in the spawned list!"));
             var client = m_ClientNetworkManagers[0];