chore: downgrade libs to make it support older version of netstandard2.1

Author: insthync

SimpleNetworkManager.NET/SimpleNetworkManager.NET.csproj

@@ -2,15 +2,15 @@
 
   <PropertyGroup>
     <LangVersion>8.0</LangVersion>
-    <TargetFramework>netstandard2.1</TargetFramework>
+    <TargetFrameworks>net8.0;netstandard2.1</TargetFrameworks>
     <ImplicitUsings>disable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <RootNamespace>Insthync.SimpleNetworkManager.NET</RootNamespace>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="MessagePack" Version="3.1.4" />
-    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="9.0.9" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.0" />
     <PackageReference Include="UniTask" Version="2.5.10" />
   </ItemGroup>