lint-and-test: Revert previous change to use latest python on MacOS.

Using '3.x' automatically selected a high single version of python on
MacOS.

However, it bumped the python version over the version that we support,
breaking with no warning - and also using different python versions
between PRs.

This is an effective revert of d8bae88.

Author: neiljp

.github/workflows/lint-and-test.yml

@@ -206,7 +206,7 @@ jobs:
           - {PYTHON: 'pypy-3.7', OS: ubuntu-latest, NAME: "PyPy 3.7 (ubuntu)", EXPECT: "Linux"}
           - {PYTHON: 'pypy-3.8', OS: ubuntu-latest, NAME: "PyPy 3.8 (ubuntu)", EXPECT: "Linux"}
           - {PYTHON: 'pypy-3.9', OS: ubuntu-latest, NAME: "PyPy 3.9 (ubuntu)", EXPECT: "Linux"}
-          - {PYTHON: '3.x', OS: macos-latest, NAME: "CPython 3.x [latest] (macos)", EXPECT: "MacOS"}
+          - {PYTHON: '3.11', OS: macos-latest, NAME: "CPython 3.11 (macos)", EXPECT: "MacOS"}
     env:
       EXPECT: ${{ matrix.env.EXPECT }}
       PYTHON: ${{ matrix.env.PYTHON }}