Revert - Multiple .NET target frameworks

Author: abhinavminhas

QueryDB.Core.Tests/QueryDB.Core.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-	  <TargetFrameworks>netcoreapp3.1;net5.0;net6.0;net7.0;net8.0;net9.0</TargetFrameworks>
+	  <TargetFramework>netcoreapp3.1</TargetFramework>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>