Update dotnetcore.yml

dotnet-version: '9.0.x'

Author: romantitov

.github/workflows/dotnetcore.yml

@@ -12,7 +12,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '8.0.x'
+        dotnet-version: '9.0.x'
 
     - name: Build with dotnet
       run: dotnet build src/MockQueryable/*.sln --configuration Release