Fail CI tests if coverage reports don't exist

Author: Exanite

.github/workflows/dotnet.yml

@@ -101,6 +101,7 @@ jobs:
               with:
                 name: coverage-${{ matrix.name }}
                 path: ./coverage/**/*.cobertura.xml
+                if-no-files-found: error
     Report-Coverage:
         name: "Report Coverage"
         runs-on: ubuntu-latest