Use consistent net6.0 TargetFramework (#1051)

This is the only project that outstands from the rest in this repo.

Author: stan-sz

tests/KubernetesClient.Classic.Tests/KubernetesClient.Classic.Tests.csproj

@@ -2,8 +2,8 @@
   <PropertyGroup>
     <IsPackable>false</IsPackable>
     <RootNamespace>k8s.Tests</RootNamespace>
-    <TargetFramework Condition="'$(OS)' != 'Windows_NT'">net6</TargetFramework>
-    <TargetFrameworks Condition="'$(OS)' == 'Windows_NT'">net6;net48</TargetFrameworks>
+    <TargetFramework Condition="'$(OS)' != 'Windows_NT'">net6.0</TargetFramework>
+    <TargetFrameworks Condition="'$(OS)' == 'Windows_NT'">net6.0;net48</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>