Adding .NET 9 build output support

Only running maven when doing a .NET 8 build as we don't want to run it in parallel, else one will fail due to file locking

Author: aaronpowell

Directory.Build.props

@@ -1,16 +1,19 @@
 <Project>
-  <!-- See https://aka.ms/dotnet/msbuild/customize for more details on customizing your build -->
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFrameworks>net8.0;net9.0</TargetFrameworks>
     <LangVersion>latest</LangVersion>
 
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <WarningsAsErrors>true</WarningsAsErrors>
 
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <PropertyGroup>
     <AspireVersion>8.2.0</AspireVersion>
     <AspNetCoreVersion>8.0.7</AspNetCoreVersion>
     <OpenTelemetryVersion>1.9.0</OpenTelemetryVersion>
+  </PropertyGroup>
 
-    <IsPackable>false</IsPackable>
-</PropertyGroup>
 </Project>

Directory.Packages.props

@@ -2,6 +2,7 @@
   <PropertyGroup>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
   </PropertyGroup>
+
   <ItemGroup>
     <!-- Aspire packages -->
     <PackageVersion Include="Aspire.Hosting" Version="$(AspireVersion)" />
@@ -28,7 +29,7 @@
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageVersion Include="xunit" Version="2.9.0" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.2" />
-    <!-- External packages -->
+    <!-- Integration packages dependencies -->
     <PackageVersion Include="OllamaSharp" Version="3.0.7" />
   </ItemGroup>
 </Project>

examples/java/CommunityToolkit.Aspire.Hosting.Java.AppHost/CommunityToolkit.Aspire.Hosting.Java.AppHost.csproj

@@ -19,7 +19,7 @@
     <ProjectReference Include="..\..\..\src\CommunityToolkit.Aspire.Hosting.Java\CommunityToolkit.Aspire.Hosting.Java.csproj" IsAspireProjectResource="false" />
   </ItemGroup>
 
-  <Target Name="PublishRunMaven" AfterTargets="Build">
+  <Target Name="PublishRunMaven" AfterTargets="Build" Condition="'$(TargetFramework)' == 'net8.0'">
     <!-- As part of publishing, ensure the Java app is freshly built -->
     <Exec WorkingDirectory="$(JavaAppRoot)" Command="./mvnw --quiet clean package" />
   </Target>