Restore net462 target for Confluent.Kafka package

Author: Havret

src/Confluent.Kafka/Confluent.Kafka.csproj

@@ -16,6 +16,7 @@
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <Title>Confluent.Kafka</Title>
     <AssemblyName>Confluent.Kafka</AssemblyName>
+    <TargetFrameworks>netstandard2.0;net462;net6.0;net8.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <SignAssembly>true</SignAssembly>