Merge pull request #9872 from Icinga/Al2Klimov-patch-5

GHA: add upcoming (already frozen) Ubuntu 23.10

Author: julianbrost

.github/workflows/linux.yml

@@ -39,6 +39,7 @@ jobs:
           - ubuntu:20.04
           - ubuntu:22.04
           - ubuntu:23.04
+          - ubuntu:23.10
 
     steps:
       - name: Checkout HEAD