Revise GitHub Actions Python versioning

Semantic versioning appears to be required now for version
specifications.

Also, PyPy appears to be done and dusted in GitHub, and I don't know
anyone using it anyway, so this patch removes it from the GitHub Actions
testing.

.github/workflows/testing.yaml

@@ -7,7 +7,8 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9, pypy2, pypy3]
+        os: [macos-latest, windows-latest, ubuntu-18.04, ubuntu-20.04]
+        python: [2.7.18, 3.5.10, 3.6.15, 3.7.16, 3.8.16, 3.9.16, 3.10.10, 3.11.2]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}