net9 on CI

Author: mgravell

.github/workflows/CI.yml

@@ -30,6 +30,7 @@ jobs:
         dotnet-version: | 
           6.0.x
           8.0.x
+          9.0.x
     - name: .NET Build
       run: dotnet build Build.csproj -c Release /p:CI=true
     - name: StackExchange.Redis.Tests

appveyor.yml

@@ -9,6 +9,8 @@ install:
     choco install dotnet-6.0-sdk
 
     choco install dotnet-7.0-sdk
+    
+    choco install dotnet-9.0-sdk
 
     cd tests\RedisConfigs\3.0.503