Pin CMake to 3.29.0 in CI for now

.github/workflows/build.yml

@@ -116,6 +116,15 @@ jobs:
       run: |
         ${{ env.SCRIPTS_ROOT }}/install-macos-deps
         xcrun --show-sdk-version
+    
+    # TODO: Remove this workaround once the `PACKAGE_PREFIX_DIR` issue is fixed,
+    # i.e. once https://github.com/microsoft/vcpkg/pull/38088 is merged,
+    # cherry-picked to Mixxx's vcpkg and once the Qt 6.5 port is updated to a
+    # version fixing https://bugreports.qt.io/browse/QTBUG-124186.
+    - name: Pin CMake to 3.29.0
+      uses: jwlawson/actions-setup-cmake@v2
+      with:
+        cmake-version: '3.29.0'
 
     # Build dependencies