Test with pypy 3.8 now that 3.7 reached EOL

Author: nicoddemus

.github/workflows/test.yml

@@ -132,7 +132,7 @@ jobs:
             tox_env: "py312"
             use_coverage: true
           - name: "ubuntu-pypy3"
-            python: "pypy-3.7"
+            python: "pypy-3.8"
             os: ubuntu-latest
             tox_env: "pypy3-xdist"