Use a container for Python 2.7

The runner for Ubuntu that supports Python 2.7 is no longer supported,
but we can still access older Pythons by using a container.

Author: pganssle

.github/workflows/tests.yml

@@ -18,26 +18,18 @@ jobs:
         os: ["ubuntu-latest", "windows-latest", "macos-latest"]
         exclude:
           - python-version: "2.7"
-            os: "windows-latest"
-          - python-version: "2.7"
-            os: "macos-latest"
-          - python-version: "2.7"
-            os: "ubuntu-latest"
         include:
           - python-version: "2.7"
-            os: "ubuntu-20.04"
+            os: "ubuntu-latest"
+            use-container: true
     env:
       TOXENV: py
-
+    container:
+      image: ${{ matrix.use-container && format('python:{0}', matrix.python-version) || '' }}
     steps:
     - uses: actions/checkout@v5
-    - if: ${{ matrix.python-version == '2.7' }}
-      run: |
-        sudo apt-get install python-is-python2
-        curl -sSL https://bootstrap.pypa.io/pip/2.7/get-pip.py -o get-pip.py
-        python get-pip.py
-    - if: ${{ matrix.python-version != '2.7' }}
-      name: ${{ matrix.python-version }} - ${{ matrix.os }}
+    - if: ${{ !matrix.use-container }}
+      name: Set up Python ${{ matrix.python-version }} on ${{ matrix.os }} (non-containers)
       uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.python-version }}