fix: replace TFM for Mapster.EF6

Author: DocSvartz

src/Mapster.EF6/Mapster.EF6.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net10.0;net9.0;net8.0;</TargetFrameworks>
+    <TargetFrameworks>net4.6.1;netstandard2.1</TargetFrameworks>
     <Description>EF6 plugin for Mapster</Description>
     <IsPackable>true</IsPackable>
 	<PackageTags>Mapster;EF6</PackageTags>