Update default TFM to net8.0

src/Tests/dotnet-new.Tests/CommonTemplatesTests.cs

@@ -263,7 +263,7 @@ public async void FeaturesSupport(
             bool supportsImplicitUsings,
             bool supportsFileScopedNs)
         {
-            const string currentDefaultFramework = "net7.0";
+            const string currentDefaultFramework = "net8.0";
             //string currentDefaultFramework = $"net{Environment.Version.Major}.{Environment.Version.Minor}";
 
             string workingDir = CreateTemporaryFolder(folderName: $"{name}-{langVersion ?? "null"}-{framework ?? "null"}");