GitHub: Hardcode .net version to 8.0.7

Author: yaira2

.github/workflows/cd-preview.yml

@@ -49,7 +49,7 @@ jobs:
     - name: Setup .NET 8
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: '8.0.x'
+        dotnet-version: '8.0.7'
 
     - name: Configure the package manifest, logo, and secrets
       shell: pwsh