ci: test on Python 3.13

That is still in beta but removed private C APIs we were using.

.github/workflows/test.yml

@@ -37,7 +37,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ["2.7", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["2.7", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12". "3.13"]
         test-suite: [python, deadlocks]
     steps:
     - name: Add deadnakes ppa
@@ -49,7 +49,7 @@ jobs:
           libpcre2-dev libjansson-dev libcap2-dev \
           curl
     - name: Install distutils
-      if: contains(fromJson('["3.6","3.7","3.8","3.9","3.10","3.11","3.12"]'), matrix.python-version)
+      if: contains(fromJson('["3.6","3.7","3.8","3.9","3.10","3.11","3.12","3.13"]'), matrix.python-version)
       run: |
         sudo apt install --no-install-recommends -qqyf python${{ matrix.python-version }}-distutils \
     - uses: actions/checkout@v4