Edit changelog for 1.7.21

ChangeLog.md

@@ -11,7 +11,9 @@
 - [`KT-53146`](https://youtrack.jetbrains.com/issue/KT-53146) JVM IR: unnecessary checkcast of null leads to NoClassDefFoundError if the type isn't available at runtime
 - [`KT-54600`](https://youtrack.jetbrains.com/issue/KT-54600) NPE on passing nullable Kotlin lambda as Java's generic SAM interface with `super` type bound
 - [`KT-54707`](https://youtrack.jetbrains.com/issue/KT-54707) "VerifyError: Bad type on operand stack" in inline call chain on a nullable array value
-- 
+- [`KT-54650`](https://youtrack.jetbrains.com/issue/KT-54650) Binary incompatible ABI change in Kotlin 1.7.20
+
+
 ### Native. Runtime. Memory
 
 - [`KT-54498`](https://youtrack.jetbrains.com/issue/KT-54498) Deprecation message of 'FreezingIsDeprecated' is not really helpful