#2221 fix netcoreapp编译问题

Author: luoyunchong

FreeSql.DbContext/FreeSql.DbContext.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
 	<PropertyGroup>
-		<TargetFrameworks>net10.0;netstandard2.1;netstandard2.0;net45;net40</TargetFrameworks>
+		<TargetFrameworks>net10.0;net9.0;net8.0;net7.0;net6.0;net5.0;netcoreapp3.1;netstandard2.1;netstandard2.0;net45;net40</TargetFrameworks>
 		<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 		<Authors>FreeSql;ncc;YeXiangQin</Authors>
 		<Description>FreeSql is the ORM in .NetCore, .NetFramework, And Xamarin. It supports Mysql, Postgresql, SqlServer, Oracle, Sqlite, Firebird, Clickhouse, DuckDB, TDengine, QuestDB, Odbc, Oledb, 达梦, 人大金仓, 南大通用, 虚谷, 神舟通用, 翰高, And Access</Description>