removed cuda 12.6 from CI, CI install seems to not work for that

Author: ingowald

.github/workflows/Ubuntu.yml

@@ -26,10 +26,6 @@ jobs:
             cuda: "13.0.2"
             gcc: 13
             config: Debug
-          - os: ubuntu-24.04
-            cuda: "12.6.0"
-            gcc: 13
-            config: Debug
           - os: ubuntu-22.04
             cuda: "12.0.0"
             gcc: 11