Use netstandard2.0 and net8.0 targets for VbaCompression library

Unit tests project must target actual .NET release so we use .NET Framework 4.8 instead of `netstandard2.0`

Implements issue #4

Author: jozefizso

src/Directory.Build.props

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <VersionPrefix>1.0.0</VersionPrefix>
-    <TargetFrameworks>net462;net48;net6.0;net7.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net8.0</TargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup>

src/Kavod.Vba.Compression.Tests/Kavod.Vba.Compression.Tests.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
+    <TargetFrameworks>net48;net8.0</TargetFrameworks>
     <IsPackable>false</IsPackable>
   </PropertyGroup>