test: use debian archive repositories for legacy python containers

Configures pytest containers to use archive.debian.org for package
installation with legacy Python versions that have outdated sources.

Author: chrisburr

.github/workflows/basic.yml

@@ -64,8 +64,10 @@ jobs:
     - uses: actions/checkout@v3
     - name: Installing dependencies
       run: |
+        echo 'deb http://archive.debian.org/debian stretch main' > /etc/apt/sources.list
+        echo 'deb http://archive.debian.org/debian-security stretch/updates main' >> /etc/apt/sources.list
+        apt-get update || true
         python -m pip install pytest mock
-        apt-get update
         apt install -y voms-clients
     - name: Run pytest
       run: pytest