Preparation for release of System.ClientModel 1.2.0 (#46410)

* System.ClientModel 1.2.0

* update CHANGELOG

Author: annelo-msft

sdk/core/System.ClientModel/CHANGELOG.md

@@ -1,15 +1,11 @@
 # Release History
 
-## 1.2.0-beta.1 (Unreleased)
-
-### Features Added
-
-### Breaking Changes
-
-### Bugs Fixed
+## 1.2.0 (2024-10-03)
 
 ### Other Changes
 
+- Upgraded `System.Memory.Data` package dependency to 6.0.0 ([#46134](https://github.com/Azure/azure-sdk-for-net/pull/46134)).
+
 ## 1.1.0 (2024-09-17)
 
 ### Other Changes

sdk/core/System.ClientModel/src/System.ClientModel.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <Description>Contains building blocks for clients that call cloud services.</Description>
-    <Version>1.2.0-beta.1</Version>
+    <Version>1.2.0</Version>
     <!--The ApiCompatVersion is managed automatically and should not generally be modified manually.-->
     <ApiCompatVersion>1.1.0</ApiCompatVersion>
     <Nullable>enable</Nullable>