Update ReleaseNotes.md

.github/workflows/ReleaseNotes.md

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 * [ManagedClient] The managed client now sends the entire topic filter including new MQTTv5 properties when subscribing.
 * [Server] Fixed reporting of _MaximumQoS_ in _ConnAck_ packet (MQTTv5 only) (#1442).
 * [Server] Fix cross thread issue in session message storage for QoS 1 and 2.
-* [Server] The event _ClientSubscribedTopicAsync_ is now fired after the subscription is completely processed internally (#1435).
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+* [Server] The event _ClientSubscribedTopicAsync_ is now fired after the subscription is completely processed internally (#1435).
+* [Server] Improved CPU usage on lower end machines (#788).
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