Update target framework in Razor integration test (#8729)

Author: RikkiGibson

test/razor/razorIntegrationTests/testAssets/RazorApp/RazorApp.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <RootNamespace>RazorApp</RootNamespace>