Add macos-latest to "pytest" CI matrix

- Use macos-13 for Python 3.8–3.9.
- Use macos-latest for Python 3.10–3.12.

.github/workflows/pytest.yaml

@@ -20,6 +20,7 @@ jobs:
       matrix:
         os:
         - macos-13
+        - macos-latest
         - ubuntu-latest
         - windows-latest
         python-version:
@@ -29,6 +30,8 @@ jobs:
         - "3.11"
         - "3.12"  # Latest supported by ixmp
         gams-version:
+        # Version used until 2024-07; disabled
+        # - 25.1.1
         # First version including a macOS arm64 distribution
         - 43.4.1
 
@@ -39,12 +42,16 @@ jobs:
         # - "==2.0.0rc0"
 
         exclude:
-        # Specific version combinations that are invalid
+        # Specific version combinations that are invalid / not to be used
         # No arm64 distribution for this version of GAMS
-        - { os: macos-latest, gams-version: 25.1.1}
+        # - { os: macos-latest, gams-version: 25.1.1}
         # No arm64 distributions of JPype for these Pythons
         - { os: macos-latest, python-version: "3.8" }
         - { os: macos-latest, python-version: "3.9" }
+        # Redundant with macos-latest
+        - { os: macos-13, python-version: "3.10" }
+        - { os: macos-13, python-version: "3.11" }
+        - { os: macos-13, python-version: "3.12" }
         # Example: pandas 2.0 requires Python >= 3.8
         # - { python-version: "3.7", pandas-version: "==2.0.0rc0" }