Use earlier image

Author: ldx

.github/workflows/build.yaml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   build-and-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         python-version:
@@ -36,7 +36,7 @@ jobs:
       run: sudo PATH=$PATH coverage run setup.py test
 
   release:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
     needs:
       - build-and-test