Implement dual targeting for netstandard2.0 and net6.0 (#276)

Author: Arkatufus

src/Akka.Persistence.PostgreSql.Hosting/Akka.Persistence.PostgreSql.Hosting.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>$(NetStandardLibVersion)</TargetFramework>
+    <TargetFrameworks>$(NetStandardLibVersion);$(NetLibVersion)</TargetFrameworks>
     <PackageIcon>icon.png</PackageIcon>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <Description>Akka.Persistence.PostgreSql Microsoft.Extensions.Hosting support.</Description>

src/Akka.Persistence.PostgreSql/Akka.Persistence.PostgreSql.csproj

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <AssemblyTitle>Akka.Persistence.PostgreSql</AssemblyTitle>
     <Description>Akka Persistence journal and snapshot store backed by PostgreSql database.</Description>
-    <TargetFramework>$(NetStandardLibVersion)</TargetFramework>
+    <TargetFrameworks>$(NetStandardLibVersion);$(NetLibVersion)</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <LangVersion>11</LangVersion>
     <PackageIcon>icon.png</PackageIcon>

src/Directory.Build.props

@@ -13,6 +13,7 @@
 
   <PropertyGroup>
     <NetStandardLibVersion>netstandard2.0</NetStandardLibVersion>
+    <NetLibVersion>net6.0</NetLibVersion>
     <NetCoreTestVersion>net7.0</NetCoreTestVersion>
     <NetFrameworkTestVersion>net48</NetFrameworkTestVersion>
   </PropertyGroup>