drop net6/net7 CI (they're EOL); add net9; net8 is preserved as LTS

Author: mgravell

.github/workflows/integration.yml

@@ -38,7 +38,7 @@ jobs:
         fail-fast: false
         matrix:
           redis-version: [ '8.0-RC2-pre', '${{ needs.redis_version.outputs.CURRENT }}', '7.2.6', '6.2.16']
-          dotnet-version: ['6.0', '7.0', '8.0']
+          dotnet-version: [ '8.0', '9.0']
       env:
         ACTIONS_ALLOW_UNSECURE_COMMANDS: true
       name: Redis ${{ matrix.redis-version }}; .NET ${{ matrix.dotnet-version }};