Sync eng/common directory with azure-sdk-tools for PR 13283 (#54414)

* bump the targeted proxy version
* bump in packages.data.props too
* resolve merge failure

---------

Co-authored-by: Scott Beddall <[email protected]>
Co-authored-by: Scott Beddall <[email protected]>

Author: azure-sdk

eng/Packages.Data.props

@@ -493,7 +493,7 @@
   </ItemGroup>
 
   <PropertyGroup>
-    <TestProxyVersion>1.0.0-dev.20250930.1</TestProxyVersion>
+    <TestProxyVersion>1.0.0-dev.20251209.1</TestProxyVersion>
     <UnbrandedGeneratorVersion>1.0.0-alpha.20251210.1</UnbrandedGeneratorVersion>
     <AzureGeneratorVersion>1.0.0-alpha.20251205.1</AzureGeneratorVersion>
   </PropertyGroup>

eng/common/testproxy/target_version.txt

@@ -1 +1 @@
-1.0.0-dev.20251022.1
+1.0.0-dev.20251209.1