Bump Confluent.Kafka from 2.6.1 to 2.8.0 (#729)

Bumps [Confluent.Kafka](https://github.com/confluentinc/confluent-kafka-dotnet) from 2.6.1 to 2.8.0.
- [Release notes](https://github.com/confluentinc/confluent-kafka-dotnet/releases)
- [Changelog](https://github.com/confluentinc/confluent-kafka-dotnet/blob/master/CHANGELOG.md)
- [Commits](confluentinc/confluent-kafka-dotnet@v2.6.1...v2.8.0)

---
updated-dependencies:
- dependency-name: Confluent.Kafka
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

src/Tingle.EventBus.Transports.Kafka/Tingle.EventBus.Transports.Kafka.csproj

@@ -10,7 +10,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Confluent.Kafka" Version="2.6.1" />
+    <PackageReference Include="Confluent.Kafka" Version="2.8.0" />
   </ItemGroup>
 
   <ItemGroup>