downgrade ubuntu to enable testing of older python versions

Author: Rami Al-Rfou

.github/workflows/pythonpackage.yaml

@@ -6,7 +6,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-22.04, macos-latest, windows-latest]
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
 
     name: Test ${{ matrix.os }} Python ${{ matrix.python-version }}