Fix unit tests

Workaround for actions/setup-python#696. macos-latest recently was updated to point to macos-14, which does not support Python 3.7, 3.8, 3.9 on ARM.

.github/workflows/unit.yml

@@ -13,6 +13,22 @@ jobs:
       matrix:
         python: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
         platform: [ubuntu-latest, macos-latest, windows-latest]
+        # Python <= 3.9 is not available on macos-14
+        # Workaround for https://github.com/actions/setup-python/issues/696
+        exclude:
+        - os: macos-latest
+          python-version: '3.9'
+        - os: macos-latest
+          python-version: '3.8'
+        - os: macos-latest
+          python-version: '3.7'
+        include:
+        - os: macos-latest
+          python-version: '3.9'
+        - os: macos-13
+          python-version: '3.8'
+        - os: macos-13
+          python-version: '3.7'
     runs-on: ${{ matrix.platform }}
     steps:
     - name: Harden Runner