Fix the CI runner to use Ubuntu 24.04.

.github/workflows/ci.yaml

@@ -9,17 +9,17 @@ on:
 jobs:
     build:
       name: run rep tests
-      runs-on: ubuntu-20.04
+      runs-on: ubuntu-24.04
 
       steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Python ${{matrix.python}}
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v5
         with:
-          python-version: 3.8
+          python-version: 3.12
       - name: Install dependencies
         run: |
-          python -m pip install docutils xmlschema
+          python -m pip install docutils pygments xmlschema
       - name: Run tests
         run: |
           make