.NET: Use TargetFramework with lowest designated net8.0 moniker

Author: amotl

by-language/csharp-npgsql/demo.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>net8.0;net9.0;net10.0</TargetFrameworks>
+    <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
     <IsPackable>false</IsPackable>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>