[dotnet-svucitl] Update target framework version for test project (#5812)

Author: imcarolwang

src/dotnet-svcutil/lib/tests/src/dotnet-svcutil-lib.Tests.csproj

@@ -4,7 +4,7 @@
     <AssemblyVersionFile>$(IntermediateOutputPath)\$(TargetFramework)\$(MSBuildProjectName).$(TargetFramework).version.cs</AssemblyVersionFile>
   </PropertyGroup>
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <NoWarn>$(NoWarn)NETSDK1023</NoWarn>
     <CLSCompliant>false</CLSCompliant>
     <IsTestProject>true</IsTestProject>