chore(ci): stay on 24 instead of ubuntu-latest

GitHub is transitioning to Ubuntu LTS 26 beginning next month.

We will stay with Ubuntu LTS 24, for now.

.github/workflows/ci.yaml

@@ -204,7 +204,7 @@ jobs:
   containerise:
     if: ${{ !cancelled() && 'success' == needs.info.result }}
     needs: ['info']
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     timeout-minutes: 30
     concurrency:
       group: ${{ github.repository }}-${{ github.workflow }}