CI: re-enable 3.8 and 3.9. Let's make those work, too...

.github/workflows/python-package.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.10", pypy-3.10]
+        python-version: ["3.8", "3.9", "3.10", pypy-3.8, pypy-3.9, pypy-3.10]
 
     steps:
     - uses: actions/checkout@v2