refactor(redis): Only cache unique dependencies in Redis cache

src/Dfe.PlanTech.Infrastructure.Redis/RedisDependencyManager.cs

@@ -27,12 +27,16 @@ public Task RegisterDependenciesAsync<T>(IDatabase database, string key, T value
     private async Task GetAndSetDependencies<T>(IDatabase database, string key, T value)
     {
         var batch = database.CreateBatch();
-        var tasks = GetDependencies(value).Select(dependency => batch.SetAddAsync(GetDependencyKey(dependency), key, CommandFlags.FireAndForget)).ToArray();
+        var tasks = GetDependencies(value).Distinct()
+                                                     .Select(dependency => batch.SetAddAsync(GetDependencyKey(dependency), key, CommandFlags.FireAndForget))
+                                                     .ToArray();
+
         if (tasks.Length == 0)
         {
             // If the value has no dependencies (is empty) it should be invalidated when new content comes in
             tasks = tasks.Append(batch.SetAddAsync(EmptyCollectionDependencyKey, key, CommandFlags.FireAndForget)).ToArray();
         }
+
         batch.Execute();
         await Task.WhenAll(tasks);
     }