Add macos-latest to "pytest" CI matrix

- Use macos-13 for Python 3.9.
- Use macos-latest for Python 3.10–3.13.
- Parallel iiasa/ixmp#532

.github/workflows/pytest.yaml

@@ -23,6 +23,7 @@ jobs:
       matrix:
         os:
         - macos-13
+        - macos-latest
         - ubuntu-latest
         - windows-latest
         python-version:
@@ -40,6 +41,16 @@ jobs:
 
         # - "3.14.0-alpha.1"  # Development version
 
+        exclude:
+        # Specific version combinations that are invalid / not to be used
+        # No arm64 distributions of JPype for these Pythons
+        - { 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" }
+        - { os: macos-13, python-version: "3.13" }
+
       fail-fast: false
 
     runs-on: ${{ matrix.os }}