Add release notes for mutex bugfix

Author: ovitrif

RELEASE-NOTES.txt

@@ -5,6 +5,7 @@
 * [**] [Jetpack-only] Block Editor: Enable VideoPress block (only on Simple WPCOM sites) [https://github.com/wordpress-mobile/WordPress-Android/pull/18440]
 * [***] Enables editing of the site homepage for sites using block-based themes directly from the pages list. [https://github.com/wordpress-mobile/WordPress-Android/pull/18454]
 * [*] Adds a button to enable account closure from the account settings screen [https://github.com/wordpress-mobile/WordPress-Android/pull/18412]
+* [*] Fixed an error when syncing offline data to the cloud. [https://github.com/wordpress-mobile/WordPress-Android/pull/18449]
 
 22.4
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