added -y switch to prevent hang during CI run

Author: Jens-G

.github/workflows/build.yml

@@ -317,7 +317,7 @@ jobs:
 #      caveat: net9 is (currently?) NOT installed, so manually again
       - name: Set up .NET SDK
         run: |
-          sudo add-apt-repository ppa:dotnet/backports
+          sudo add-apt-repository -y ppa:dotnet/backports
           sudo apt-get install -y --no-install-recommends dotnet-sdk-9.0
 #      end