Run GHA on both 3.9 and 3.13

Author: zware

.github/workflows/build.yml

@@ -10,13 +10,18 @@ env:
 jobs:
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version:
+          - '3.9'
+          - '3.13'
     steps:
       - uses: actions/checkout@v4
         with:
           persist-credentials: false
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
-          python-version: 3.9
+          python-version: ${{ matrix.python-version }}
       - name: Check configuration
-        run: make check PIP=pip BUILDBOT=buildbot
+        run: make check PIP=pip BUILDBOT=buildbot PYTHON_VERSION=${{ matrix.python-version }}