CI: Force Python 3.11 on Mac runner

.github/workflows/rolling-release.yml

@@ -326,6 +326,11 @@ jobs:
       with:
         fetch-depth: 0
 
+    # Python 3.12 removed distutils, used by MoltenVK -> glslang.
+    - uses: actions/setup-python@v4
+      with:
+        python-version: '3.11'
+
     - name: Install packages
       shell: bash
       run: |