[PR #7820/536c80e2 backport][3.9] Bump pypy to 3.9 (#7823)

**This is a backport of PR #7820 as merged into master
(536c80e).**

We're getting a lot of segfaults when initialising the tests with Pypy
recently. Maybe bumping to a more recent release will help (3.8 is near
EOL anyway).

Co-authored-by: Sam Bull <git@sambull.org>

.github/workflows/ci-cd.yml

@@ -137,7 +137,7 @@ jobs:
           - os: windows
             no-extensions: 'Y'
         include:
-          - pyver: pypy-3.8
+          - pyver: pypy-3.9
             no-extensions: 'Y'
             os: ubuntu
             experimental: false