upgrade doctest to ubuntu-24.04

Author: Damien-Chen

.github/workflows/reusable-docs.yml

@@ -99,7 +99,7 @@ jobs:
   # Run "doctest" on HEAD as new syntax doesn't exist in the latest stable release
   doctest:
     name: 'Doctest'
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     timeout-minutes: 60
     steps:
     - uses: actions/checkout@v4