bump pypy to 3.8

Author: minrk

.github/workflows/test.yml

@@ -66,7 +66,7 @@ jobs:
             zmq: bundled
 
           - os: ubuntu-22.04
-            python: pypy-3.7
+            python: pypy-3.8
 
           - os: ubuntu-22.04
             python: "3.9"