Update CI matrix os and exclusions

Author: EliahKagan

.github/workflows/tox.yml

@@ -6,15 +6,32 @@ jobs:
   tox:
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-13, macos-14, windows-latest]
+        os:
+        - ubuntu-22.04  # Used only for testing Python 3.7.
+        - ubuntu-latest
+        - macos-13
+        - macos-latest
+        - windows-latest
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
-        exclude:  # Exclude builds that are not currently available.
-        - os: macos-14
-          python-version: '3.7'
-        - os: macos-14
+        exclude:
+        # Exclude unnecessary Ubuntu 22.04 runs.
+        - os: ubuntu-22.04
           python-version: '3.8'
-        - os: macos-14
+        - os: ubuntu-22.04
           python-version: '3.9'
+        - os: ubuntu-22.04
+          python-version: '3.10'
+        - os: ubuntu-22.04
+          python-version: '3.11'
+        - os: ubuntu-22.04
+          python-version: '3.12'
+        # Exclude builds that are not currently available.
+        - os: ubuntu-latest
+          python-version: '3.7'
+        - os: macos-latest
+          python-version: '3.7'
+        - os: macos-latest
+          python-version: '3.8'
 
       fail-fast: false