Update AutoRest C# version to 3.0.0-beta.20230912.3 (#38653)

Author: azure-sdk

eng/Packages.Data.props

@@ -174,7 +174,7 @@
     All should have PrivateAssets="All" set so they don't become package dependencies
   -->
   <ItemGroup>
-    <PackageReference Update="Microsoft.Azure.AutoRest.CSharp" Version="3.0.0-beta.20230907.2" PrivateAssets="All" />
+    <PackageReference Update="Microsoft.Azure.AutoRest.CSharp" Version="3.0.0-beta.20230912.3" PrivateAssets="All" />
     <PackageReference Update="Azure.ClientSdk.Analyzers" Version="0.1.1-dev.20230822.1" PrivateAssets="All" />
     <PackageReference Update="coverlet.collector" Version="3.2.0" PrivateAssets="All" />
     <PackageReference Update="Microsoft.CodeAnalysis.NetAnalyzers" Version="7.0.1" PrivateAssets="All" />

eng/emitter-package.json

@@ -1,6 +1,6 @@
 {
     "main": "dist/src/index.js",
     "dependencies": {
-      "@azure-tools/typespec-csharp": "0.2.0-beta.20230907.2"
+      "@azure-tools/typespec-csharp": "0.2.0-beta.20230912.3"
     }
 }