fix: update the hash code for the list so it can be retrieved from dictionary correctly (#2390)

Author: seanamorosoamtote

src/Confluent.SchemaRegistry/Rest/DataContracts/Schema.cs

@@ -271,12 +271,37 @@ public override int GetHashCode()
             unchecked
             {
                 var hashCode = SchemaString.GetHashCode();
-                hashCode = (hashCode * 397) ^ (References != null ? References.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ (References != null ? GetListHashCode(References) : 0); 
                 hashCode = (hashCode * 397) ^ (Metadata != null ? Metadata.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ (RuleSet != null ? RuleSet.GetHashCode() : 0);
                 return hashCode;
             }
         }
+        
+        /// <summary>
+        ///     Returns a hash code for a list of objects.
+        /// </summary>
+        /// <param name="list">
+        ///     The list to get the hash code for.
+        /// </param> 
+        /// <returns>
+        ///     An integer that specifies a hash value for this instance.
+        /// </returns>
+        private int GetListHashCode<T>(IList<T> list)
+        {
+            if (list == null || list.Count == 0)
+                return 0;
+
+            unchecked
+            {
+                int hash = 0;
+                foreach (var item in list)
+                {
+                    hash += item?.GetHashCode() ?? 0;
+                }
+                return hash;
+            }
+        }
 
         /// <summary>
         ///     Compares this instance with another instance of this object type and indicates whether