Test PyPy 3.9, reduce number of Python interpreters in CI pipeline

Author: dolfinus

.github/workflows/test.yml

@@ -34,7 +34,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.7', '3.8', '3.9', 3.11.0-rc.1, pypy-3.7, pypy-3.8]
+        python-version: ['3.7', 3.11.0-rc.1, pypy-3.7, pypy-3.9]
         os: [ubuntu-latest]
         # run only limited set of tests because it takes too long
         mark: [important]