Fixes issue of mac-os environment not supporting python 3.9 issue as …

…described here: actions/setup-python#850

.github/workflows/python-package.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest, macos-13, windows-latest] # Update to macos-latest when https://github.com/actions/setup-python/issues/850 has been resolved
         python-version: ["3.9", "3.10"]
 
     steps: