Revise GitHub Actions Python versioning

Semantic versioning appears to be required now for version
specifications.

Updated checkout to v3 (whatever that means)

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.

Author: marshallward

.github/workflows/testing.yaml

@@ -7,9 +7,10 @@ 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
+    - uses: actions/checkout@v3
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v2
       with: