Fix CI

Author: bbc2

.github/workflows/main.yml

@@ -2,10 +2,10 @@ name: main
 on: [push]
 jobs:
   check-tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ['3.7', '3.11', 'pypy3.8']
+        python-version: ['3.7', '3.11', 'pypy3.10']
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5