Update RELEASE_NOTES.md for 1.4.40-RC1 (#268)

Co-authored-by: Aaron Stannard <[email protected]>

Author: Arkatufus

RELEASE_NOTES.md

@@ -1,3 +1,7 @@
+#### 1.4.40-RC1 July 1 2022 ####
+* [Fix HighestSequenceNr query not returning proper value](https://github.com/akkadotnet/Akka.Persistence.MongoDB/pull/267)
+* [Bump MongoDb.Driver to 2.16.1](https://github.com/akkadotnet/Akka.Persistence.MongoDB/pull/266)
+
 #### 1.4.39 June 6 2022 ####
 * [Bump Akka.NET version to 1.4.39](https://github.com/akkadotnet/akka.net/releases/tag/1.4.39)
 * [Fix compatibility with Akka.Cluster.Sharding in persistence mode](https://github.com/akkadotnet/Akka.Persistence.MongoDB/pull/259)