Revert .NET bump for build-ilspy.yml

Author: ds5678

.github/workflows/build-ilspy.yml

@@ -34,7 +34,7 @@ jobs:
 
     - uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: '9.0.x'
+        dotnet-version: '8.0.x'
         dotnet-quality: 'ga'
       env:
         DOTNET_INSTALL_DIR: ${{ runner.temp }}/.dotnet