Make sure Python 3.8/3.9 compatibility tests run on CI

Author: abravalheri

.github/workflows/main.yml

@@ -16,6 +16,11 @@ jobs:
         - ubuntu-latest
         - macos-latest
         - windows-latest
+        include:
+        - platform: ubuntu-latest
+          python: ~3.8.0-0
+        - platform: ubuntu-latest
+          python: ~3.9.0-0
     runs-on: ${{ matrix.platform }}
     steps:
       - uses: actions/checkout@v3