Update Microsoft.Extensions.AI.OpenAI version reference (#1456)

Author: stephentoub

Directory.Packages.props

@@ -67,7 +67,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageVersion>
-    <PackageVersion Include="Microsoft.Extensions.AI.OpenAI" Version="10.2.0-preview.1.26063.2" />
+    <PackageVersion Include="Microsoft.Extensions.AI.OpenAI" Version="$(MicrosoftExtensionsVersion)" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="$(System10Version)" />
     <PackageVersion Include="Microsoft.Extensions.Hosting" Version="$(System10Version)" />
     <PackageVersion Include="Microsoft.Extensions.Logging" Version="$(System10Version)" />
@@ -94,4 +94,4 @@
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
     <PackageVersion Include="JsonSchema.Net" Version="9.1.3" />
   </ItemGroup>
-</Project>
+</Project>