#1479 Rework conditional packages in v6 branch

Have added net 6 as a TFM and implement conditional packages

Author: thompson-tomo

projects/RabbitMQ.Client.OAuth2/RabbitMQ.Client.OAuth2.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net462;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net462;netstandard2.0;net6.0</TargetFrameworks>
     <NoWarn>$(NoWarn);CS1591</NoWarn>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <AssemblyTitle>RabbitMQ OAuth2 Client Library for .NET</AssemblyTitle>
@@ -59,6 +59,9 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
     <PackageReference Include="MinVer" Version="4.3.0" PrivateAssets="all" />
+  </ItemGroup>
+
+  <ItemGroup Condition="$(TargetFramework) == 'net462' OR $(TargetFramework) == 'netstandard2.0'">
     <PackageReference Include="System.Net.Http.Json" Version="7.0.1" />
     <PackageReference Include="System.Text.Json" Version="7.0.2" />
   </ItemGroup>

projects/RabbitMQ.Client/RabbitMQ.Client.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net462;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net462;netstandard2.0;net6.0</TargetFrameworks>
     <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings>
     <NoWarn>$(NoWarn);CS1591</NoWarn>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
@@ -62,10 +62,10 @@
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
 
     <PackageReference Include="MinVer" Version="4.3.0" PrivateAssets="All" />
-    <PackageReference Include="System.Threading.Channels" Version="7.0.0" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
+  <ItemGroup Condition="$(TargetFramework) == 'net462' OR $(TargetFramework) == 'netstandard2.0'">
+    <PackageReference Include="System.Threading.Channels" Version="7.0.0" />
     <PackageReference Include="System.Memory" Version="4.5.5" />
   </ItemGroup>