Upgrade to pypy-3.9 in unit tests

Author: miguelgrinberg

.github/workflows/tests.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python: ['3.7', '3.8', '3.9', '3.10', '3.11', 'pypy-3.8']
+        python: ['3.7', '3.8', '3.9', '3.10', '3.11', 'pypy-3.9']
         exclude:
           # pypy3 currently fails to run on Windows
           - os: windows-latest