gh-128504: Upgrade doctest to ubuntu-24.04 (#128506)

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Hugo van Kemenade <[email protected]>

Author: 3 people

.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