Use 8.0.x in build-test

Author: danielmarbach

.github/workflows/build-test.yaml

@@ -14,6 +14,11 @@ jobs:
         uses: actions/checkout@v4
         with:
           submodules: true
+      - name: Setup .NET SDK
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: |
+            8.0.x          
       - name: Cache NuGet packages
         uses: actions/cache@v4
         with: