Update Azure.ClientSdk.Analyzers.Tests from net6 to net8 (#9011)

Author: JimSuplizio

src/dotnet/Azure.ClientSdk.Analyzers/Azure.ClientSdk.Analyzers.Tests/Azure.ClientSdk.Analyzers.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net6.0</TargetFrameworks>
+    <TargetFrameworks>net8.0</TargetFrameworks>
     <TargetFrameworks Condition="'$(OS)' == 'Windows_NT'">$(TargetFrameworks);net472</TargetFrameworks>
     <PreserveCompilationContext>true</PreserveCompilationContext>
   </PropertyGroup>