Fix native collections leak on Unity v2021+

Assets/com.vladfaust.unitywakatime/Editor/Plugin.cs

@@ -149,7 +149,8 @@ static void SendHeartbeat(bool fromSave = false) {
         operation => {
           if (request.downloadHandler.text == string.Empty) {
             Debug.LogWarning(
-              "<WakaTime> Network is unreachable. Consider disabling completely if you're working offline");
+              "<WakaTime> Network is unreachable. Consider disabling completely if you're working offline");
+            request.Dispose();
             return;
           }
 
@@ -172,7 +173,9 @@ static void SendHeartbeat(bool fromSave = false) {
           else {
             if (_debug) Debug.Log("<WakaTime> Sent heartbeat!");
             _lastHeartbeat = response.data;
-          }
+          }
+
+          request.Dispose();
         };
     }