Install .NET 9 RC in the pages pipeline (#43)

Install .NET 9 RC in the pages pipeline so DocFX can run correctly.

Author: richardsondev

.github/workflows/pages.yml

@@ -28,6 +28,12 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+  
+      - name: Setup .NET Core SDK
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '9.0.x'
+          dotnet-quality: 'preview'
 
       - name: Setup Pages
         uses: actions/configure-pages@v5