Add more recent Python versions to test matrix (#15)

* Add more recent Python versions to test matrix

* Pin CI to ubuntu-20.04

.github/workflows/main.yml

@@ -6,16 +6,16 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ["3.5", "3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.5", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v4
 
       - name: Set up Python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}