main.yml: bump pypy to latest stock version (3.10, because 3.9 seems to have sporadic timing issues anyway)

.github/workflows/main.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9, '3.10', '3.11', pypy3.9]
+        python-version: [3.6, 3.7, 3.8, 3.9, '3.10', '3.11', pypy3.10]
       fail-fast: false
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps: