feat(CI): use the Ubuntu 20.04 container to build PythonMonkey itself

Author: Xmader

.github/workflows/test-and-publish.yaml

@@ -140,6 +140,7 @@ jobs:
         os: [ 'ubuntu-22.04', 'macos-13', 'macos-14', 'windows-2022', 'ubuntu-22.04-arm' ]
         python_version: [ '3.8', '3.9', '3.10', '3.11', '3.12', '3.13' ]
     runs-on: ${{ matrix.os }}
+    container: ${{ (matrix.os == 'ubuntu-22.04' && 'ubuntu:20.04') || null }}
     steps:
       - uses: actions/checkout@v4
         with: