PHPLIB-1175: Use container with Python 2.7 for building docs

Author: jmikola

.github/workflows/docs.yml

@@ -20,6 +20,8 @@ jobs:
   giza:
     name: "Build Docs"
     runs-on: "ubuntu-20.04"
+    container:
+      image: python:2.7.18-buster
 
     steps:
       - name: "Checkout library"
@@ -35,11 +37,6 @@ jobs:
           path: docs
           fetch-depth: 2
 
-      - name: "Setup python"
-        uses: actions/setup-python@v4
-        with:
-          python-version: '2.7'
-
       # The requirements file installs urllib3 with an incompatible version; we replace it with one that works
       - name: "Install giza"
         run: |