test: make changed2 always differ from original2 in collection generators

With RandGenBool an overwrite keeps the existing value half the time, so when
no elements were added or removed, changed2 could equal original2 and the
"do not match" assertions failed. Each overwrite now redraws until it differs
from the original element.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Tests/Runtime/NetworkVariable/NetworkVariableTests.cs

@@ -1870,6 +1870,11 @@ public string ArrayStr<T>(NativeArray<T> arr) where T : unmanaged
             {
                 var idx = rand.Next(changed2.Length - 1);
                 var item = generator(rand);
+                // Ensures changed2 differs from original2 when its length matches original2.
+                while (idx < original2.Length && EqualityComparer<T>.Default.Equals(item, original2[idx]))
+                {
+                    item = generator(rand);
+                }
                 changed2[idx] = item;
             }
 
@@ -2165,6 +2170,11 @@ public string DictionaryStr<TKey, TVal>(Dictionary<TKey, TVal> list)
             {
                 var idx = rand.Next(changed2.Count - 1);
                 var item = generator(rand);
+                // Ensures changed2 differs from original2 when no elements are added or removed.
+                while (EqualityComparer<T>.Default.Equals(item, original2[idx]))
+                {
+                    item = generator(rand);
+                }
                 changed2[idx] = item;
             }
 
@@ -3663,6 +3673,11 @@ public string NativeHashMapStr<TKey, TVal>(NativeHashMap<TKey, TVal> list)
             {
                 var idx = rand.Next(changed2.Length - 1);
                 var item = generator(rand);
+                // Ensures changed2 differs from original2 when no elements are added or removed.
+                while (EqualityComparer<T>.Default.Equals(item, original2[idx]))
+                {
+                    item = generator(rand);
+                }
                 changed2[idx] = item;
             }