🚧 GitHub Actions: Fix testing for Python 3.6

.github/workflows/test.yml

@@ -10,13 +10,15 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false
       matrix:
         python-version: [ "3.6", "3.7", "3.8", "3.9", "3.10", "3.11" ]
 
+    # For Python 3.6, we need to fall back to Ubuntu 20.04
+    runs-on: ${{ matrix.python-version != "3.6" && "ubuntu-latest" || "ubuntu-20.04" }}
+
     env:
       test_results_dir: test-results-${{ matrix.python-version }}